I note that many many of the posters to this thread are Unregistered Guests or New Members. The Shadow Shopper debate goes on and on and on. I never registered with them and never intend to, yet I do believe they can be a useful tool for new or would-be shoppers who don't have the time or internet knowledge to seek out the contacts for themselves. This is not a bad thing in and of itself but for many would be a useless expenditure.
Lets look at logic and human nature for a moment. MSPs and schedulers will not put out the effort to post good jobs in places beyond their own website if they have a shopper base to fill the jobs without the extra effort. Heck, my Bestmark scheduler uses promises of her good jobs as a carrot on a stick to get you to take the schlock. A good job, IMHO, is one that has reasonable requirements for the pay (fee + useful reimbursement) offered. The good jobs are things such as a grocery store job I do that is nearby pays $13 fee and reimburses up to $20 in groceries. That, after expenses, is a $30 benefit job for me, takes little more time than my regular trip to do the grocery shopping anyway and takes about 20 minutes to do the report. Those jobs NEVER get listed on Jobslinger.com or the job boards of other places and if you happen to see them because there was a heads up posted by a shopper, I can assure you that they have been taken already. So unless Shadow Shopper is paying MSPs and schedulers to post all their shops there, I can't imagine why they would.
The next question, of course, is the shopper base. Some MSPs lose active shoppers over issues such as pay and disclosure of the depth required for a shop. I no longer shop for some MSPs with attractive looking shops because when they say they pay in 30 days and it is several months later and I am still calling and sending emails to get paid, that is not worth my time or aggravation. Some MSPs lose active shoppers because they advertise a job as ABC and when you have signed up and gotten to the paperwork it is A-Z+1-5. Thanks, but no thanks. Some MSPs lose active shoppers because the shops I did last year for $15 fee only now are $12.75 for the same job. Need I say more?
I personally have found that job boards are most useful for finding MSPs that do shops in my area and signing up with them not for the current job but for future ones. And my best jobs come from email and phone calls from schedulers who offer the job at one fee and if they can't find someone to take it, call on shoppers with whom they have a history at a more reasonable fee.