For me, face is one of the major parts physically that i am attracted to, so i get why someone would like seeing someones face in a nude pic, but...

That being said, if you are uncomfortable, don't do it. Your reasoning is more than valid. Sadly, what you fear indeed happens quite often. And he should get that. Trust needs to be earned.

Me and my girlfriend have a system. If she sends me a nude, it gets deleted the next time we see each other. Face or no face. Ofcourse, that still requires her to trust i don't copy it anywhere else, so this system also requires a lot of trust. Not something done with someone you can't trust.

There is another option, what comes to systems for this, that i have used in the past. Mutually assured destruction. He wants a nude with face, he sends a nude with face. He leaks your pics, you leak his pics kinda thing. Taking into consideration local laws about revenge porn, ofcourse. Ill advised if there are laws for it.

Point is, do what you are comfortable with, and nothing else.