Some tattoo artists are very talented, however the pictures they're showing you in their book is not always the reality. Indeed, most of the time, tattooists are taking a picture of a fresh tattoo, not a healed tattoo.
In some cases, you can have some surprises when you see the tattoo a few months or a few years later. Either the customer did nothing to heal correctly, either the artist don't use a good ink or don't tattoo deep enough. And the result can be poorly (even if we have to say that most of the time, it is the fault of the customer who don't apply enough pomade).