Tattoo Booking Challenges

A few challenges I faced this month:

A client asked me to touch-up another artists work. Is that considered disrespectful to the artist? Does the intention of ‘fixing’ alleviate thoughts around vandalism? I decided to not follow through with booking the appointment. I may need to think of this further ~ 

A client asked me to tattoo a flash piece in an area where i thought it would not work. I struggled with this before and ended up tattooing the design anyways - the experience was very different/difficult, it took longer, it felt like endless labour. Trust your guts? Should this discomfort suggest not following through with requests as such in the future?