I've had to ban a handful over the years. Not many, considering how many I've known personally or via the forum over the years, but it's never a good feeling when someone dirties up your community. (And I am not, for the record, suggesting that is the case in the present thread.)
I agree that paying up front is generally a bad idea. The couple of times I've done so, (that come to mind), both ended badly. (But I was made whole in each instance after a bit of arm twisting.)