NEW TRY FOR AN ARTICLE:
Trashing is mostly strong - even more with Dark Ages on-trash-abilities. A card like Lookout is correctly priced at $3, though it trashes "in the dark" - a card saying "+1action, +1card, trash a card" is probably even better and would cost at least $3, too.
The latter doesn't exist in Dominion, but there are two 5$ versions, namely Junk Dealer and Upgrade. Upgrade additionally gains a card costing exactly 1 more than the trashed card, while Junk Dealer includes a vanilla peddler. Thus, buying JD provides two cards roughly worth $3 and $4 for the price of 5$. Is it too cheap?
The downsides
Cost/value relation isn't linear: $3+$4 is far from $7, and sometimes $3+$4 is even less than $5. In other words, the major downside of Junk Dealer is its opportunity costs: many cards at the same price give more specific advantages, changing the nature of the game, e.g. cursers.
The second downside: trashing isn't optional. This leads to typical problems of mandatory trashers: If your opponent plays discard attacks, you don't know what to keep in hand; if you are close to the end, your good-card/bad-card ratio increases and trashing becomes less useful; and it antisynergizes with other trashers, as your JD will soon lack of target. Just take note of two exceptions:
- you can trash-for-benefit Junk Dealers in the late game
- if you use Steward/Count as a trasher only a single time, there is enough junk left for JD
Synergy of trashing and peddling
Now that we have seen why Junk Dealers two abilities are sometimes less than the sum of their added value, the question remains when cantrip trashing and peddling work together at their best. Both lead to higher average buying power, therefore Junk Dealer boosts your probability to reach $5 or $6 every turn. This makes it most worthy if you want to build up an engine with expensive components, especially because trashing is crucial in engine building. This even includes buying a single JD before buying a couple of minions, laboratories or stables.
Another interesting option is to boost mediocre BM-strategies. JD itself is a lousy BM-enabler, but being nonterminal, it can be combined with nondrawing terminals bought at a 3-4-start, some examples: While BM-Swindler or BM-Scavenger are rather weak strategies on their own, adding a Junk Deaker turns both into a viable challenge.
Synergies
On-trash-abilities
Expensive engine components
Antisynergies
Opponents hand-reducers
Other trashers (excluding tfb)
FIRST VERSION
Hi, i am new on this forum, and i haven't found an article about Junk Dealer, though it's one of my favourite cards. So i tried to write one myself, do with it whatever you want to 
I am interested in your opinions about it. By the way, i apologize if you find mistakes or strange phrases - i am not a native speaker.
JUNK DEALER
Maybe, this powerful card is so severely underrated because of the art on it: look at this poor, ugly guy! He has to sell trash to get a single buck! Doesn't look sexy at all. Though, it is.
Why is this card so strong?
Simply put, because nonterminal trashing is strong. Cantrip trashing is even stronger; and additionally, you get a coin for it. What do you want more? Maybe, you'll want some impressing abilities for 5$, but likewise with JackOfAllTrades, it's the sum of four mediocre advantages which turns out to be strong.
Now, this time, Junk Dealer is nonterminal, and like all nonterminals, it only really shines if there are other cards in game you can cooperate with. Of course, the first thing coming to mind is its abilty to enable engines: You can thin your deck, but neither will Junk Dealer slowdown your economy nor is it terminal. But it can do more than this:
Assisting Cursers and Looters
Clearly, reliable Junk Attacks remain the strongest cards in the game, and if you let your opponent give you ten ruins or curses just to clean them out with Junk Dealer, you'll end up in big trouble. You need one of those cursers – or maybe two of them?
If we are talking about chainable Cultists or Familiars, you should get a second one. Maybe this also holds with Mountebank, as they keep on junking after the curses are out, and the risk of a collision is clearly lower than with two witches due to spamming coppers and lack of card-drawing. In a game with IGG's, you should buy some copies of them until your opponent gave you enough targets (curses) for buying a junk dealer; maybe, if you have three or four, the chance is high enough to prefer the junk dealer.
The other cursers and looters– witch, young witch, sea hag and Marauder – should probably be bought only once due to the risk of terminal collision.
And, here we go – after you have bought your curser(s), Junk Dealer will be your best friend. In a game with mountebank or IGGs, you might even get a second one because of all those nasty coppers.
Assisting strong nonterminals
One might question the necessity of a Junk Dealer due to the high opportunity cost: Isn't it better to go with Hunting Parties, Minions or Labs? Probably yes - if you weren't allowed to buy different 5's. But the big deal is to get the best of both worlds:
If you buy a junk dealer first, then starting the hunting party, both cards will come up more often and become a devastating engine. Even better is the combo "first a junk dealer, then go minions". Just have a look at the well-known combo Minion – Loan. Similarly, a junk dealer can clean out coppers without being terminal; and it has two more synergic abilities: it trashes estates/shelters, and it can decrease your hand size.
Both together compensate sufficiently for the opportunity cost of 1 Minion.
Now, how does it work with labs? These one have "+card" instead of "+coin, trash a card", which is clearly weaker at the beginning of a game and stronger in the end. So, just start with junk dealer and buy labs afterwards, and you'll be fine.
A big money approach
We all know about the strength of Masquerade-BigMoney. In the beginning of the game, Junk Dealer does a very similar thing: If we set aside funny card-passing, it gives you +1coin instead of +1card, which isn't weaker in the first turns.
Later on, the additional card will outclass the extra-coin; and furthermore, if in the late game all your cards are strong, junk dealer can be a dead card due to mandatory trashing. Thus, simply going BM will be weaker than with Masquerade.
So, the question is: can these weaknesses be compensated by being nonterminal? I think, on many boards, the answer is "yes". If you don't get junk dealer with a 2-5-opening, you might want to start silver+terminal. The latter one doesn't need to be as strong as a swindler or a sea hag; say, a cutpurse or even a navigator might do it as well. All these increase your chances to get $5 in round 3 or 4.
Later on, you might want to buy a second terminal; having a bigger deck, the risk of collision decreases, and it is even 33% lower than with masquerade, as junk dealer can't draw dead other cards.
Furthermore, some cantrips might be nice-to-have. Ahead of all, the synergy with market square should be mentioned here. Just don't overdo buying actions, remember that we are talking about a big money approach - so don't come up with Villages or gainers, you will just be wasting your time.
Summed up, with reasonable sidewings, i think JunkDealer-BM might be stronger than Masquerade-BM.
Cooperating with other trashers
Junk Dealer works fine with the remodel family. While at the beginning, deck tuning will be fast, later on you can trash-for-benefit your junk dealer.
It also cooperates in a nice way with flexible trashers: Its a good idea to use a Steward as trasher only a single time and let junk dealer do the rest. The same holds for Count.
Weaker trashers, say a loan or a lookout, should simply be ignored when junk dealer is out; merely, you might skip it compared to other strong trashers, e.g. chapel or counterfeit. Depends on the kingdom ... as it always does.
Antisynergy with discarders
The best reason to skip junk dealer are strong discard attacks.
First, if you get attacked, you have a difficult choice: Keeping the junk dealer with two good cards is risky, as you might have to trash one of these if your drawn card is even better. Keeping Junk Dealer with a good and a bad card to trash might end up silly as well, if your next card doesn't help you. Maybe the best thing to do is keeping the three strongest cards and discard the Junk Dealer; but of course, this is not why you have bought it.
Second, discard attacks like margrave, Torturer or Ghost Ship are simply stronger.
And third, as all of the above draw cards, Junk Dealer might get drawn dead, which is no good fundament for seminal cooperation.
Other reasons to skip junk dealer
Better 5$-cards which don't need a junk dealers assistance. But, beside the already-mentioned, there aren't many. Clearly wharf, probably apprentice. Vault also doesn't work with Junk Dealer, but it's hard to say which is better.
In addition, it is weak in terminal draw-big money and garden games. And dukes don't like it when copper gets cleared out. Though, on many boards these strategies can be topped by a different approach which includes junk dealer.
Maybe the most common reason to buy other things is, that drawing exactly five bucks comes up too late. Trashers need to work early, and especially junk dealer doesn't like the endgame when lack of trashable cards make it unplayable.
And if you plan to go Junk Dealer but find $6, Gold might often be the better deal.
And of course, you will rarely need a second one (perhaps, in Mountebank games, you do).
Summary
Junk Dealer is good for BM and engine-building, and a helpful assistance in games with Junk-Attacks. It is weak in Terminal-Draw-BM and against discard attacks.
Synergies
Market Square
Good components for engines or nondrawing BigMoney
Antisynergies
Discard attacks
Wharf
