You do not have to fill in each tattoo perfectly. A general covering is enough for the game to log the tat as done and move on.
Ink
Do not prod or poke the tattoos. Doing so will only cause your subject pain and will result on them giving up. Instead, try and literally stroke the ink on.
Swapping
Swapping customers around really is important. You only need temporarily swap the order to keep everyone happy, just doing enough to calm them down before moving on.
