The phrase "top bidder" refers to the person who offers the highest amount of money or makes the highest bid in an auction or competitive bidding process. They are the one who is willing to pay the most for something. Full definition
The Japanese have long been big on such Western sports as baseball, golf, bowling and even horse racing (for the past couple of years they have been top bidders at thoroughbred sales in the U.S. and Britain), but now they may have gone one step too far toward sports insanity: they have taken up baton twirling. (si.com)
A Beagle pup won in a local Cincinnati event nearly two years ago had three homes within two days because neither of the two top bidders really wanted it. (canismajor.com)