stupid people until you find out you sold something for $10 that you later found out was worth thousands

It's that what OP shops or St Vinnies is for?

I'm just trying to get rid of all of my dead roommate's shit. We've been selling super nice shit for pennies on the dollar because we aren't trying to get rich, we just want it done and a little bit of cash to cover the rent he didn't pay.

This is much better than throwing away things (even if they're not junk when we have to make room to buy new items we can't live without...)
Somehow like circular economy, I like it

Love me a rummage sale.

Garage sales are awesome! They are places where people sell stuff that is perfectly fine but they don't have a use for anymore at reasonable prices.

Sure, they also try to sell a bunch of crap too, but garage sales are a great way to circulate stuff around the community for reuse.