While a glitch in the matrix kept me from participating in the online bidding this year, I did so last year and had a rather unpleasant experience...
There was one lot I actually won, a Scottish dirk on which I was the high bidder when the hammer dropped, and I received an acknowledgement of such - I even have the screenshot showing I was the high and final bid.
And then, the next day, when I realized I hadn't yet been charged for the lot, I checked the hammer prices, only to find they showed the hammer price to be $25
below my bid to a floor bidder.
That pissed me off a little.
Now, I attend enough auctions in person (1-2 a month, every month) to know that the auction house wants to show a little love to the bidders who take the time and effort to attend in person. I've seen auctioneers drop the hammer a little early, or offer a very slight incremental increase to the floor. But this - a full day after the fact - was IMO unacceptable.