Why sometime tattoo and piercing shops say – NO.
If you ever get refused a service in tattoo or piercing place there might a good reason for it. First of all it might legal issues like persons age or being under influence of something or some countries there placements on body or symbols or procedures that are not legal.
Other reason in piercing would be health issues in terms piercing not suited for specific anatomy of piercing being more cool than safe in general.
In tattooing same rules apply and none of respectable tattoo artists wants to brake law or do bad work either it is design that is impossible to do or it is a placement where tattoo would work for design or skill of artst