Prepare your son to have uncomfortable conversations with adults. Kids need to learn the fine art of being able to stand up for themselves while also being respectful. Many kids can communicate via social media but I don't think most of today's teenagers are good on the phone. or in person. And some of these coaches are hard-core and use pressure sales tactics on kids.
Teach your child how to text/email properly. One college coach added my 2020 on Snapchat and just yesterday on his story, the coach posted an email he received that was somewhat poorly written. While I think it was in poor taste for this coach to make fun of it, I also know that this coach will never consider this kid to be part of his program. I don't think there's anything wrong with proofing your child's email/texts to a coach until you're sure they can do it on their own.