The Tahitians taught the sailors the craft who in turn taught it to other sailors, and that is why tattoo is often associated with sailors. There are health risks that are attached to getting a tattoo. The tattoo needles need to be sterilized after each use by using proper sterilizing equipment. There are standards set out by The Alliance of Professional Tattooists which the professional tattooist should follow. Getting tattoos done by professionals who adhere to these rules will minimize the health risks.
Chances are better if the ink was injected on the same level.
Size and location of the tattoo. Newer ones are harder to take off. How well the person will heal from the removal procedure. Total and complete removal is never guaranteed. The pain from getting a tattoo is far less than the pain of getting it removed.