The only people I know of who have had problems went to scratchers. This is becoming a big problem with the availability of guns and supplies all over the internet dirt cheap and the increasing popularity. Post on a Facebook garage sale type page you are looking for tattoo artist recommendations and you'll find hundreds of responses offering themselves or their brother to do it from their home. Even if they think they are sterile, a professional artist in a licensed studio knows how to do a quick skin reaction test with the ink and also uses higher quality products than scratchers pick up off eBay.