I asked a similar question a while back on here but was more focused on record keeping. I'm posting from my phone so searching for it right now would take a while. I remember some people using pre made documents from Jantz or someplace like that. Basically just fill in the blank, hopefully you have decent handwriting. Maybe make a template up in MS Word and print it out on nice paper.
I think if you had blade steel, handle material, HT specs, pattern name, any extras (file work, colored spacers, bolsters, etc...) and a birth date/completion date you should have most of the bases covered. Oh and what type of grind, hollow, flat, chisel, whatever. A nice touch might be a separate care and warranty sheet. How to store, clean, protect, and sharpen are the basics I guess. Don't forget your contact info and I always like to see an actual signature in blue ink, kinda personalizes it. For a special knife maybe some pics of the making of it. People like to know where these things come from.
I know it can be a lot of work, but you really need to put yourself into a sales mindset. Anything you can do to make the customer feel like you are going the extra mile just for them will help eliminate buyers remorse. Someone who had to fight to get in touch with you, or questions where their money is going will pick apart every detail and complain. A personalized certificate that can only go with their knife will make some of these customers just a little bit happier. (none of this scenario is directed at anyone in particular, just an example)
These are just some of my thoughts after having worked years of retail in all kinds of products.
just my .02¢
-Xander
