If it were for a friend of mine, I'd just do it for free, and be done with it. If it's not a close friend I wouldn't touch it.
The probability of a poor cure or over-cure is almost nonexistent if you properly weigh and calculate your ingredients. The problem comes from issues that may arise once they leave your hands; Improper storage, temperature issues, sanitation at the final location..... Too many possibilities to name, but if you had benefited in any way when something goes wrong, you can bet you will be named as the bad guy or maybe even sued if someone gets ill from other issues beyond your control.
Your close enough to Amish country there, if he's not a good enough friend to have him over to make the cure mix and start the curing process, then send him down the road to an Amish butcher/store. Put any liability into his hands not in yours.
