Hi
The first question you have to ask yourself is
Were you happy with the first artist? (EG sterility, quality of work etc)
If you were go back to him and the touch up should be free – the artist is right it is not uncommon to need small touch ups on a big tattoo.
It is when the ink flushes out in huge patches and it looks shit you should worry.
If you were not happy with the artist for X reason a new artist should be able to do a touch up no sweat and they shouldn’t take more than an hour – usually a lot less (30 mins) depending on the work.
Remember do not skimp on the price of ink – it is there for life and you want it to look fantastic.
Take Care
Matthew