It is all dependent. What I mean by dependent is that it doesn't matter how much time the artist blocks off but how long it actually takes and how good the artist's service is. It also depends on if you plan on seeing this artist more than once. I have gone to same artist before 3 times and tipped him well each time b/c he was that good and everytime you go back, he will remember you as an individual and not just another person coming in to get work done. I have also only tipped about $5.00 on a tattoo that took more time to prep than complete and only cost $40.00 total to begin with. As for always tipping, I would say it depends again b/c it is such a delicate and permanent thing that you are getting done but if the final product sucks, you have a lot more things to worry about than the tip!