I check my role before accepting the fp/ops, and if it's wrong, I decline. Simple.
This for me as well.
Playing since early access, and only ever happened once. I was on my sin, and early on had both tank and dps selected as there is very little difference sub level 30 and had up to date generator and shield on me at all times, but later on, when you are actually more specialised, I forgot to uncheck the tank role. I apologise and left.