I can't speak for everyone but I must say the fact he was laughed out of the shop is the best sign that they were not the right people to work with and unprofessional. Cover ups are common, people make mistakes, especially at 17. I have done many cover ups, and In my day have got old ugly tattoos from my youth lasered and covered. I think you should just keep searching and find the right shop and artist that is more receptive to your friends needs. Certainly your friend should not be made to feel stupid for his/her decision to get a cover up or the concept for that cover up. Now that said, an artist may direct the design in the best way to cover what is existing as well as what will work for a tattoo given its size and placement ect. cheers.