I was a "barker" for a time (the person doing the auction on the courthouse steps). My client did not allow me to even follow a buyer to the bank (many banks just a block away) and get a check. The Buyer had to have a cashiers check in hand the moment the auction concluded. For that reason, none of my auctions sold to anyone other than the entity forcing the sale (typically the primary mortgage holder).
The above advice is about right. Very few are tax sales, but tax sales do get complicated quick. In addition, there are rights of redemption in some states for tax sales. You're best bet is to have a title attorney do a title search and find out what and how many liens may affect a property prior to you bidding.