We've been gazumped and I'm still majorly pissed off about it. The EA has blathered on about being under a legal obligation to pass on offers but said that the gazumpers knew that an offer had been accepted but chose to gazump anyway. Personally I don't think I could do it and nor would I, as a vendor, be a dick.
The EA said it's actually not that common these days but not sure how true that is.