I did mystery shopping for a couple of years. I started when I had only one DS. In a nutshell, some assignments were fun, the report writing was mostly boring and the fact that you spent hours to perfect a report and couldn't bring your kids were negatives.
Some of the visits were fun i.e. visit a bank and pretend to open a savings account and ask a set of questions. Write a report - get $30. Sometimes I visited a clothing store and had set questions to ask. But mostly it was fast food and you had a set amount of questions and things to observe.
And the report writing - unless it was an essay-style report, I found the writing very very dry and tedious. I had to write essay-style answers about Pizza Pizza food, for example. It sounds okay but trust me - the reports were very boring.
The assignments were too labour intensive. It would take me 2 hours or more to do a report. If the report is not perfect, they just don't pay you for the assignment.
So here is the biggest negative - at least within the company for which I worked - when you take on an assignment, you are required to cover out-of-pocket expenses. You will be reimbursed for the expenses but only after your assignment has been read and accepted. If you don't get all the correct information, you miss a detail or your report is not written correctly - they will either request more details or reject the entire thing.
So when I would see, for instance, a Mystery Shopping assignment at a Niagara on the Lake spa - I'd kind of be nervous. Sure - you get a night in a hotel and spa treatments for free - but you must pay for those things yourself first and then only after the assignment is accepted, are you reimbursed.
There would, therefore, be stress about whether you'd actually have the assignment accepted or would you end up spending money!
And as I said, no kids and the exotic assignments were only for experienced shoppers who has passed numerous levels of exams and minor assignments.
I actually would still be doing the assignments because I had great fun doing the retail and banking ones but they seemed to dwindle and eventually my city only seemed to have Pizza Pizza assignments! And I don't like Pizza Pizza!
Oh yes - I'd have to find someone to watch my kids, I'd drive to the assignment, I'd do the assignment. Then I'd bring home the food (you're not supposed to do this but there is no way I could or would eat all that food) to share with the family. THEN, I'd spend about 1 - 2 hours writing my assignment (that is again, without kids). Then I'd get paid perhaps $8-12 and reimbursement for the food.
I guess if you really like fast food, it's okay but I really didn't care if I had a free meal of New York Fries or Pizza Pizza!
Also - some of the other assigments (i.e. visiting a pub or restaurant) involve two adults. So you could bring a friend (but again if you have children, they can't come).
The last detail I recall - I had a strict timeline. You had about 24 hours to submit your report. So - if I went to a scheduled visit at 1pm., I had until the next afternoon to submit my write-up. So again, I had to plan the visit around my family's schedules.
It was a lot of hassle. My DH still misses the free fries though.