The fact that this person had to come in and ask is exactly why I don't use them. I really can't quantify how many sales I would lose if I watermarked. But I do know I used to be asked this a lot by potential buyers that I directed to my sites.
I keep telling people this happens (sorry Patrick, this in no way reflects against you at all....I was unsure when I joined but don't tell anyone) but, nobody ever believed me