Have you looked at bid history, as reason should be shown.
Usually they use "entered wrong amount" but they should then enter the correct amount. They are abusing the system but no means to report this. In any case knowing they abuse the system, would you want them as a buyer?
Just retracting costs you nothing, but buying, paying and then inventing faults to return at your expense costs money.
Add bidder to your blocked bidders list.
