"If you meant that he put his initial bid WHILE having a -ve balance, then this is a technical issue"

Yes he actually did. And I have evidence as I took a screenshot before he started bidding, during the bid and after he won the bid and his balance was unchanged.

Anyway, based on what you explain, I hold Nordeus responsible for providing unreliable information when showing the bidding opponent's balance as it cos me 30+ tokens.
I would never have gone on a bid against someone with unlimited tokens if, on top of that, he had unlimited credit.

I always check my opponent before bidding to avoid such things.