Over here in the UK, we tend to label these shops as two different entities, it is either a pawn shop where the item is pawned for cash, and redeemed again when cash is available to get it back. The shop gives a time limit so if the item is not redeemed within say a week, it then goes on sale to the general public.
The other type is a genuine second hand shop where you take unwanted stuff that you don't want back and hopefully get a reasonable price for it, the shop puts it up for sale straight away, or at least after cleaning and checking it out.

However, I have obtained a few brass instruments via the second hand shops, mainly because there is something odd about them and not instruments that would see normal brass band use here in the UK. From an early Chinese imported Lark cornet, horribly tinny sound with an oversized mouth piece receptor, to a two valved soprano marching bugle from America in the key of G.
I did also find a so called pocket trumpet on a second hand market stall in Switzerland during a holiday there. It doesn't play, it is an Indian made brass ornament stamped with the name Besson and son London. Bringing it back into the UK was possible the first time it had ever been near London.