Do a search for “Tattoo Television” on Youtube and you’ll find a number of good videos under their channel. Though they are intended mainly for tattoo artists, they can give you some idea of what you can ask your artist to see if they know what they are doing. For example:
1) The brightness of a tattoo is determined more by it’s color strategy than by the pigments used
2) A design can be made bolder not by using more black, but by using it in just the right places
3) Tattoo artists who work in other artistic mediums are usually better at what they do