It's simple, the thrill of "winning" at all costs.
I've known people who had an addiction to it and needed intervention.
What really makes me roll my eyes is that stratosphere guy on ebay. His prices are insane. He sells necks and bodies for about what i can get the whole guitar for looking at graigslist or such. he'll sell a mexi resissue neck for $350-400 and i have seen the entire mexi reissue in GL many times for that or just a bit more. But people are willing to buy from him thereby enabling him to inflate his prices. If people stopped buying from him for even a few days his prices would have to drop like a rock or he'd be out. The guy IMO is a prifce gouger because he has a sort of monopoly on FENDER strat parts and he knows it.
People get caught up in the moment.. just like at a Pawn Shop, they often overpay without doing any research or looking around, it's called instant gratification, spur of the moment buying.
There are lots of folks addicted to auctions, it becomes a competition for them on some level.
Man I wish some of these rampant overpayers would come across my auctions.
Seems like I can't give stuff away and settle for pennies on the dollar right now. And it's not like I'm selling garbage or anything.
Yeah, but can you blame him? If people keep buying from him, why would he stop.