Jim
Yes, you can get caught up in the excitement of buying something at an auction and getting carried away and bidding more than the item is worth.
Also, depends on what kind of auction you're going to - but seeing as you've mentioned a couple where the items are generally very very expensive I'll add some comments
1. Car Auctions - depending which auction you go to, take someone who KNOWS cars very well indeed to ensure you don't buy a lemon. Set yourself a maximum bid price and STICK TO IT no matter what. Arrive early to view cars on the stock list you are insterested in. Be prepared to watch as cars go by and are sold for what you think is higher than you'd think
2. House Auctions - You've really got to do your homework for these - you've also probably got to have the finance in place prior to the auction too. House auctions in the UK are around, but even then, the 'auction' value of a house/property more often than not FAR exceeds what most average earners can afford anyway - hence the auctions are dominated by investors, buy to let landlords, those with plenty of cash to spare.
Yes, overall you can pick up a bargain at auction, however you also REALLY need to know your stuff (certainly for the above 2 examples) before you go, and whilst you're there. I've bought a Van at an auction and after I won, i was literally shaking like a leaf with the buzz of it all and the fear of if it was a good one or not (turns out it was good!)
Cheers! DtM! West London & Slough UK!