Been to a lot of auctions both live and online. Ordinarily if you really screw up it can take days or weeks for the true depth of your "buyers remorse" to set in, but with an auction you get that awesome sick feeling INSTANTLY!!!I have participated in an online auction.
Like ANY auction, KNOW the item worth, fees and what you are willing to spend.
Not being prepared and disciplined will cost you $$$$$. Be willing to let it go.