I had some of the same concerns going into making hets and co-dom hets, but it's been pretty easy going so far with 23 of the 30 100% hets I produced this season sold or on payment plans.
Reputation is very important, photographing lock ups and ovulations and egg laying and anything you can to document the pairing will help.
Providing signed photographic genetics guarantees is something I expect when I buy any snake that is a het, I know my customers expect it also.
I do up the document, print it out, sign it and then scan it and re-print it to place in the box with the snake and I also email it to the customer should they want a digital copy.
Honesty, good customer service, QUALITY animals, good pictures(pictures sell) and being out there in the reptile community will go a long ways towards making people comfortable with buying from you.