If that weird feature is legal at all, it should at 
the very least take out the top bidder's bid and 
restore the second highest bidder's original 
bid. 

Example: I'm leading the auction at 12,000 yen 
with a max of 30,000 yen and another bidder 
wins it at 31,000. If the seller cancels the top 
bidder, I would only buy it at 12,000 and not at 
my max. I believe that's the fairest solution. 
And I shouldn't be obligated to buy it, if I 
choose not to.

How do I know that the top bidder isn't in 
league with the seller? Sorry, I'm just really 
suspicious with things like this.