... 2nd hand store ... they want $2 each ... I should go offer a lot price, since they always seem to be there ...
You don't ask, you don't get ... but the management of a collectibles shop includes more than just moving goods at a profit.
Rather like the old cameras in a photo shop window, or an old sewing machine in a cloth shop window, the old postcards have value as eye candy: they make a shopper stop & look, which gives them a chance to slow down & buy.
Moreover, there is the issue of price point. If they are calling themselves an antiques shop, they may not want a customer to ever leave the store having spent less than a dollar. And it is always good for business to have a few things that are over-priced ;)
Lastly, of course, the cards do not take a lot of room, and the shop owner may not care if they dribble out, one-by-one. After all, it is the happy buyer who is the most likely to come back, and look again.
Okay ... I'm spending way too much time hanging at my local collectibles shop. The owner, BTW, spends his days, every day, constantly re-arranging his stock, so that the regulars notice new things, even if they are not new.