I've been a mystery shopper off and on for at least five years, only doing it intermittently for extra cash between other jobs, but now, out of necessity, I am beginning to take it on with more full-time efforts.
I've learned a few things over the years.
Firstly, in Maine at least, there is no one mystery shopping company that can provide enough jobs to make a decent amount of money; I have joined dozens of companies however, and can patch together enough assignments from various companies to make a route on a certain day that makes it a little more worthwhile.
Secondly, I've learned to simply pass on jobs that first get listed. Any job that pays less than $20 is simply not worth it. When you factor in the time to prepare, the time to do the shop and the time to complete the survey post-shop (including uploading of documents and images), a shop rarely takes any less than one hour -- unless it is a type of shop you have done already and can skip all the preparation. I have found that it is of benefit to not take assignments when they first get posted and instead wait, and wait, and wait, until the due date deadline looms, at which point the assignment will be offered with bonuses and a $20 assignment can quickly turn into a $50 assignment as the recruiters get desperate to have their jobs filled.
Thirdly, it seems most efficient when you can line up 5-10 shops in a cluster in the same area and do them all on the same day. This is the only time when i might consider taking a $20 assignment -- when i have some $100, $85 and $50 assignments in a locality, and tagging on a couple $20 assignments that are in the neighborhood is doable because i'm already spending gas and time on other shops that make it worthwhile.
These are my first introductory insights I can offer as a newbie to this group. I look forward to learning more tips from the pros!
-Ben from Maine