DS had gloves available, and he wore them while shampooing her hair although she gave him an 'odd' look when he put them on.
You know, I'm wondering if this was part of the problem too.
Now, of course, the OP's DS had every right to wear these gloves. I'm not saying he shouldn't have put them on, odd look from the client or not.
But I have to say that if I walked into a salon, and there were many people around me getting haircuts and shampoos by ungloved stylists, and my stylist put some on to deal with me, I might be a little put off. If I was getting a color treatment or perm or something else chemical, I probably wouldn't even notice the use of gloves, but for a cut and shampoo? I would feel uncomfortable, I think, if I was the only one that seemed to require gloves-even if in my heart of hearts, I knew that yes, my hair or scalp condition required them.
Now, of course I'm not advocating that no stylist wear gloves ever. What I do think is that it would be better if everyone in the salon always wore gloves, if some did sometimes. This would be more respectful of all clients, and also it is true that some scalp conditions might not be as obvious as others and you might want gloves even if you don't think you do, KWIM? It would benefit both client and stylist, I think.
Not that the OP's son had any control over this in that situation but maybe one day he will, when he gets out into a job in a salon or even his own salon, and might want to consider a universal glove use policy.