I have an EIN (for my tutoring business) but I ignore all the MSCs requests for them (there haven't been that many).
I don't do TS shops (all they have around here is some daddy's toilet pizza, which I refuse to do). They used to have shops for a competitor of Subway, but I don't see those. If I were bidding on a job (I am not even sure what that means, re: mystery shopping) I would put in the bid with the following information (just off the top of my head!)
My fee.
Payment Terms 50% up front/50% upon completion of the work
Conditions under which I will work
Conditions under which additional payment will be required (one edit taking 30 minutes or less included in the original fee; 15% of original fee for each additional edit.
Time frame in which I will get the job done. Depending on the scope of the job, etc.
An explanation (boiler plate) that as an independent contract I will get the word done as in the manner I determine is the best course of action...and this shall include, if necessary, sub-contracting work.