Hello, I did the unfortunate bid.
The error came when I was usisng PIP (picture in picture) on my monitor and didn't really see what was going on, just going like it was with BO.
Then I contacted live support ingame and was advised to start a support case. The case was promptly closed with usuall "sorry can't do".
Yes, it seems all bids are final, because trade wasn't final at this stage. It finalized 1d9h hours later as per Mindark decision. Certainly was enough time to act, not that seller got the money in an instant like in other auction mistakes. And I don't think he expected such a bid and would be wronged by bid reversal.
Now I wait for seller to come online, but it seems he seldom plays the game. Maybe I will see some decency after all. Anyway, I will leave the game in near future. Thank you all for support.