Thrift store over-pricing issues: maybe size does matter

Since I'm trying not to become a hoarder, I've been bringing donations when I go thrifting.  Recently, I damaged a large stainless steel double boiler when I left it on the stove for too long and all the water in the bottom boiled off.  I cleaned it the best I could with steel wool but couldn't get rid the burn marks on the bottom part completely, plus the plastic on the handles looked a bit deformed and it was a bit warped on the bottom so it no longer sat flat on my stovetop.  Nevertheless, it was still functional and the top part, where you put the food, was undamaged, so I decided to donate it.  Well there it was sitting on the shelf the next time I went to that goodwill.  I originally paid around $20 retail for it and they priced it at $12.01!  I was completely shocked!  I understand that they don't and can't know the price of everything, but this was a no-name, made in china, pot that was obviously not in perfect condition.  I really wonder what criteria they use to price things!  The only thing that this pot had going for it was that it was quite a large pot...