Market is a +Buy peddler. That's not that strong, is it?
It's pretty strong. +Buy is useful in a lot of cases, and it's important in almost every engine. When you're building an engine, you'd often get a Market over a lot of other +Buy cards, since it doesn't take up any space in your deck and gives some virtual money to boot. If Peddler is a strong $4 card, I'd say Market is a pretty strong $5 card - not top-tier, but somewhere in the middle of the (rather strong) $5 pack.
So I actually had Market on exactly the rank it got on this list, but there's one thing I don't understand. What makes Market better on average than Seaway? If there is a cantrip that costs $4 or less that you want, which happens often, wouldn't you rather buy a Seaway? In the cases where you want a lot of +Buy, you can get it cheaper this way, since you only have to buy Seaway once, then you can buy (or gain) the cheaper card at its usual price. Of course you may then not get the +$1, but you get whatever the card provides, maybe something you need more, like +Actions or draw. Even if there's not a good target cantrip, if there's any $4 card you want to play every turn (and don't have all the copies of it you want yet), buying Seaway is basically a $1 Market Square that doesn't even cost a Buy (but competes with other $5s). Maybe I way overrated it, I had it around rank 40, but is it really that bad? And its combo with Highway is too good! (That says more about Highway, true, but still.)