Used GP's of almost any kind tend to go for $375-425 shipped. You can buy new GP's right around $500, and they VERY RARELY go for much less than $400 used, in any configuration. That's assuming it has the correct box and paperwork. $350-400 if it's gun only and it's in good shape.
Local shops right around $400. Of course your negotiating skills and friendliness of the shop can play a part in any sale.
There's nothing to worry about with a used GP, nothing can hurt them.