It depends on status. Some accept them for free, some you have to pay them, others just don't accept them at all within reason. As for me, I accept them as long as there's an entry saying that I am.

And now with the advent of Patreon, it has made getting requests even harder I assume.
Even if you give a person making a request a sketch, that little gesture of kindness could mean the world to that person making a request.