This disorder is associated with several vascular, neurological, and skeletal problems including stroke, heart attack, clotting, mental retardation, eye abnormalities, and osteoporosis, amongst many other complications.
Tattoo tipping etiquette, in general, should hover around 15% for small tattoos and 20% for larger tattoos, but as with all tips, you as a customer ultimately determine the amount based on the quality of service and the work performed. Consider your involvement as well.
I have tattoo of palm trees and stars, it cost me $70, it's about half the size of a dollar bill. Just answered a question similiar to this one. Depends on the place, design, how much ink, detail, color, shading, etc. Don't shop tattoos, shop for an artist. Find an artist you like and besides peace of mind from knowing you made an informed decision from looking at portfolios, reputation, friends, and talking to different artists.