In the modern era, I don't see what the issues are.
As a buyer, just tell the seller that you'd like to take his picture on your phone, as a bit of added security, as you've had a bad experience of buying from someone unscrupulous in the past. ( A little white lie, of course)
Tell him you'll be deleting it in a week or two.
If the car you're buying is legit and he's nothing to hide, then he's nothing to worry about.
If he won't let you take his pic. Don't buy the car. Simples.