Ray, I deal with this with phone calls almost daily, so I feel your pain.
What I have found is they guy has gotten bad advice from a forum and now stripped the car and is already through the primer stage and that last thing he wants to hear is “sand it off” While I’m at it there are a lot of good forums out there but there are a couple where bad advice is the norm and endorsed by the forum owners in their own way.
One will not let you challenge bad advice and another owner is pushing a snake oil.
At this point, the guy really does not want to hear what I have to say but the truth be known, he has doubts and that is why he called.
What I do is go deep into the why and what can happen and explain how the chemicals in that situation can react, perhaps more then they want to hear but I will go a step further and say, you have a “say” 70% chance of getting away with what you have and give him a time frame of when it could happen, such as yesterday, I told the guy, it may blow first four hours in sun, 6 months or last three years, so you decide the risk.
Cheaper and easier to sand primer off now, then sanding paint and buying more paint down the road., I also try and explain, I have no dog in this fight, just giving you an honest opinion.
If you state it in black and white, they do understand.