I’m not going to say what, but I sold something on eBay for a couple of hundred to a buyer, I’ve since discovered that they have sold it on for over £1k.
I did my research and looked at previous sold things of the same type and I thought it would go for more then £100/£200. But I’m kicking myself now.
It’s not really an AIBU. It’s more of a venting as I’m angry at myself.