nope, as many times as you want as long as someone has outbid you.
do yourself and wait until the last minute of the auction and bid, using a sniper program. Just search google for ebay sniper. that program will place a bid for you in the last <10 seconds of the auction. that way, you don't bid up the price of an auction in the meantime (get into a bidding war with another bidder).....establish what you are willing to pay for the item and use the sniper program.....