Does anyone use these? Got any tricks or tips? Do you have to use a new brush for each person? If not how do you clean your brush? Do you have a release form for people to sign that keeps you free from anything that happens, like if they scrub it off in the shower, if they have an allergic reaction to the paint etc? Does this service affect your insurance? What do you charge, how long did it take you to get pretty good at it, and do you offer any kind of guarantee about how long it will last? Thanks for any info!!