I was doing a large number of Five Guys shops one bit of advice I can offer is to do a few for the offered price then wait and see if the call you. I was getting 10-15 bucks per shop plus the food cost. I was doing 2-3 on every weekend. I actually had to stop as my Cholesterol was going up and I was going to be able to deduct the pills as a business expense. Most of the Five Guys did a good to very good job. Those that did not always had changes the next time I visited. There was one store where they were not doing proper food safety and I told them when called I would not shop that location again. After a few months I did go back and all was fine.
I never had any push back on any negative comments.
My only issue was that sometimes I wanted to write MORE than I could as they limit how long the comments can be.