Do shops that sell used bikes normally also sell used parts? Background

I'd like to buy some used bike parts.

I don't want to shop online. I'm not very good at bike repair. I want to ask the seller if the part is the right shape and size to fit my bike. If they say "no", then I'll know not to waste my money and time buying it and trying to install it. If they say "yes", and it turns out not to fit, then I can get a refund without paying for return shipping.

I know that I can definitely buy used parts from a bike co-op. In fact, because co-ops disassemble so many bikes, they tend to have a better selection of used parts than most bricks-and-mortar vendors.

But I live in the suburbs. I'd rather not schlep downtown to get to a co-op.

There are two different individuals in my neighborhood who fix bikes in their backyards and sell them out in front of their homes. Perhaps they'll have the parts I need. But perhaps not.

Another possible alternative for me would be to go to a local bike shop.

My question

What's the general rule? Do bike shops that sell used bicycles normally also sell used parts?
They likely have "extra" bike parts around that are scavenged from bikes that were unrepariable, just be sure you know what your getting. There likely isn't any warranty included on used equipment, so if it was a "distressed" part that finally breaks a week after you've been using it, you be replacing it again. If you trust the bike shop and it is a reputable store that's been around for awhile, you should be fine. Nothing wrong with used parts, just so it fits and works correctly for its intended design, and doesn't appear to have been abused or been on a bike that was not maintained or has been wrecked.