A disclaimer isn't acceptable if there is a reaction. A client isn't qualified to make the decision not to have a patch test and as the professional we are supposed to guide them.
As soon as a client even talks about having any treatment that requires a patch test, we patch test them, then at least we know it's done with our products. We make a note of the date etc then if the client wants a treatment, the patch test is done.
But you're right, I've been having my professionally coloured for years and never ever been patch tested!
Vic x