Yes, there is indeed such as thing as a bad buyer. Sales people can't understand it but customer support people sure can. My friend Bob has a great post on this.

He writes,

How many of you have been burned by a customer who shouldn't have bought your product but did? When a company spends perfectly good money on a vendor solution it doesn't need or can't possible use successfully, the vendor loses more than the buyer - because buyers have this strange habit of talking to each other.

Go read Bob's post. I can't think of anything to add (although I really ought to say something about the Speedo).