Heya Smee,
It does happen quite a bit actually, which is not so pleasant.
It seems that its a bit of fee avoidance for the seller. I am currently selling some Mag Wheels and have had plenty of offers to end the auction early and they all *suggest* that its a great way to get out of paying ebay fees.
I sell quite a bit of stuff and have only ended 1 large auction early, it was a dead laptop and the fella offered me a ridiculous amount of money, it was way more than I expected to get so I jumped at the offer. Also, he couldnt leave me crap feedback if he got the laptop and couldnt fix it (which I carefully explained in the listing).
So, yes! it seems to happen heaps.
Lexie