How do you swap contact details? eBay block most obvious permutations, and they do reprimand sellers, if not the buyers.
And yes, I would do that, because if someone ever did that to me I’d leave them negative feedback, and then I’d not buy off someone with recent negative feedback, and that’s probably worth a lot more than £9. I really do think you’re in the minority.
I’ve never cancelled an auction (why would you?!), and never had one cancelled on me. The house analogy doesn’t really stand. If you had to present a letter to an estate agent saying that you’d reneged on your last deal would you still do it as keenly?
As a buyer you lose nothing other than being a massive nuisance, as a seller you stand to lose more. It’s really short sighted not to see that.