I can guarantee we feel just as awful when it happens! Biting is awful and yes sometimes it can be prevented, but often it can't, unless you totally isolate the biter that is. I can also guarantee that the parent of the biter feels terrible when their child is biting others too (well not always but most often).

I once had a parent say 'what sort of parent raises a biter' to me when his child was bitten, um, the parenting has nothing to do with it.