Jen, no doubt you've been reading what everyone has been saying about simplicity.
My opinion? 100% hets. are just that- 100% guaranteed- and should be easy for anyone to prove out.
If your paperwork includes these things:
-Pic of Sire
-Pic of Dame
-Pic of offspring being guaranteed
-Declaration of genetics
-Guarantee that the genetics are correct (you can throw in all of that stuff about what you will do if the animal does not prove out, but why? You have already guaranteed the animal - if the original buyer is not happy with the animal it is most likely because they want to get out of breeding or have replaced it with a visual.)
-Your contact info and signature
-Weights, dates, etc if you'd like
If your paperwork includes these basic things you should be alright. Too much clutter and the buyer will start looking for loopholes if they are a dink.
As far as 50% hets. go... you could do the same thing without the genetic guarantee and simplify the declaration of genetics to something like "This animal has a 50% possibility for carrying the "X" gene. We cannot conclusively guarantee this animals genetics without breeding it."
If I am going to buy an animal from you, you are going to have my money in your hand before I see the paperwork (since the animal would have to be shipped)... so obviously I've instilled some level of trust in you beforehand. Make the customer feel comfortable and they will be content with whatever level of paperwork you provide. That is why some of the "big boys" get away with not sending any paperwork... people trust them.