Someone from the psa boards sent me an e-mail and asked me if there were any dealers that I would unequivocally vouch for that I am confident do not alter cards.
On the message boards, I can recall five I have bought from that I would vouch for.

Jay Wolt
Luxury Wines
Dan Markel
Joe Tauriello

I have bought cards from them all and would have no hesitation about buying from any of them in the future.

Anyone's omission from this list does not suggest anything positive or negative about them....only that I cannot recall any more dealers that have been on the message boards that I have bought from.