My Apolgies, I wasn't trying to be snarky.

I just have found that I sleep better when I don't take on projects that are outside my comfort zone, and sometimes I do tell a client, I am not familiar enough with X to feel comfortable for either you or I, and if you will approve it I will ask a (professional colleague), to deal with this part of your situation for this year.

That way I can sleep well, keep most of the client's work, and be certain that the new complication is taken care of comprehensively.