It is pretty easy for a B-crat pin to work, but most of the time it takes several cards.
For a straight B-crat pin you need to play 5 B-crats and have the other guy be unable to do anything about it. Doing that means that you need to be able to absorb or trash 5 Silvers.
Shrugging off mass silver gain can actually be surprisingly easy:
5 Princes of B-crats will work easily, but normally the game is long over by the time you get there. One fast setup is Heavy trasher (e.g. Chapel, Steward)/B-crat/Quarry/$2/+buy (Festival, Woodcutters, Bridge, etc.); you can surprisingly quickly get to the point where every other turn you will Prince a B-crat. With no draw you can then efficiently take all the remaining VP in the game.
Likewise Kc/Scheme or Kc/Scavenger will also let you shrug off silvers. Kc x3 -> Sch x2 -> B-crat x2 will pin an opponent & adding in a third Sch will let you buy a province. This is, however, very slow for Kc games of this type and Kc/Sch or Kc/Scav handily defeats a lot of B-crat pins.
To a degree, you can draw through the silver with cards like Hparty or Golem; normally this breaks the pin quick when you draw 5 silver, but use of Scheme or top decking (e.g. Mandarin) can work here.
A few big draw strats (like Rogue/Hermit or Chouse/Cellar) can also power through the silvers, but almost always when you can do that, you can just do those strats for something faster than B-crat pin.
So trashing silver is another option. Masq is nice, you can hand over an estate, draw two cards and trash a silver. Mercenary is also nice - you draw 2, trash 2 so each B-crat play takes an extra 1/2 action on net. Bonfire is handy as long as you have +buys & draw. Apprentice can get decent draw from the Silver. For mass trashing while using other draw, well Forge& Count are insanely good as long as you do not start to fall behind on silver trashing. B-crat pins are also one of the few places where it can be worth it to have a second Chapel.
As with any pin, there are a number of enablers that can make it much stronger:
Discarders make it so you have fewer B-crats to play; Ghost ship and Minion are particularly strong as they cannot just discard Green out of reach of your B-crat.
Outpost to double the efficiency of the deck at pinning if you can draw deck.
Mission, the better version of Outpost, but you must generate $4 per turn.
Rabble, Fortune teller, and Haunted woods are also particularly helpful for setting up B-crat pins.
