MysteryShopSmart.com

Pros:

Gapbuster does have a very high number of jobs available due to the size of its largest client. Even rural shoppers are likely to have shops available in their area at times. In addition, Gapbuster often offers bonuses for shops that are not completed in a short amount of time.

Gapbuster also has a pretty website, complete with a job board that bumps bonused jobs to the top.

Cons:
Gapbuster's basic shop fees are often too low for the amount of work requested, though the reimbursement amounts are fair. In particular, the extensive training programs for each project should necessitate higher fees due to the time investment; however, Gapbuster won't even allow you to search for shops before taking their certification program, and most shops start under $10 before bonuses.

I find that the website has gone too far with its bells and whistles, making it less usable. It is really necessary to have to look at every shopper update for the last 3 months just to access the job board, and then again have a detailed list of every shop I'm qualified every time I try to search for shops? It would be much better if these notifications just came up the first time, or had a check box to not display them again.

Their mystery shopper incentives are rather patronizing.  Offering "a chance to strike gold" or "hidden treasure" - basically, hidden bonuses inside shops that you don't know about until afterward - are not typical for independent contracting work and do not portray shoppers as professional.