In my opinion, if they ARE possible hets produced from proven hets, at that weight the price is fair market value if they do have true markers. As I've mentioned over and over and over, there is more to it than just a "clear" belly and posterior belly stripes. I've had normals with "striped" bellies as some have said, but they are not the same as pied markers. The marker IS real. Yes, not all hets have the markers, but when shopping for pos. hets, it is a VERY GOOD indicator of a het. A 100% het female at 600 grams would be in the $600-800 range...and more depending on who you buy from. I've also seen normal females at 600 grams for around $100 on average.
I also want to add, EVERY SINGLE 100% het pied and VERY LARGE number of my 66% and 50% possible hets have the markers. EVERY Pastel het Pied I've produced had the marker. There is a reason Pete Kahl sold all of his 100% hets and kept all of his possible hets for breeding stock. He is the largest producer of Pieds in the WORLD because he knows what to look for. He sold what was going to make him more money while knowing which pos. hets were actually hets. He is not the only "big" breeder that buys stock in the het pied marker theory.
Please don't take my post as offensive. It is not meant in that way at all. As others have also mentioned, know who you are buying from and know what to look for. Do your research and make sure you are able to take a loss should it not prove to your satisfaction. Both of my original hets purchased in 2003 have very strong markers and have passed it on to all hets as well as many possible hets including 66% and 50% pos hets. Reputation goes a long way and I never recieved paperwork with my hets, nor have I ever had to provide paperwork with any of mine. If it's requested, I would be happy to provide it as I'm sure any well respected breeder would too.