And really the notion I try to get across here is to first try the companies such as the blue portal of Market Force, Corporate Research and these days Bare International. These companies offer at least SOME work everywhere. They are not the most lucrative companies to work with in the long run. They offer pretty decent job specific instructions so frankly it is hard to have a report rejected unless you really do it wrong.
Preparation time for any shop takes the longest the first time you do it and preparation time for the first ever shops will also take longer. These companies are likely to have multiple locations to perform the same shop, so the smart shopper will try additional locations after they did a shop the first time and it was accepted just to see for themselves how much less time is involved in subsequent shops the second or third time around.
Length of time for payment and amount of out of pocket expense to be reimbursed are deal breakers for many shoppers. Market Force pays monthly around the 10th, I believe Corporate Research pays twice a month and Bare monthly around the 15th. There are companies that pay faster and companies that pay a whole lot slower, but these generally do not have shops everywhere.
There is little point in signing up with a whole lot of companies until you decide how you feel about shops. There are a whole lot of folks who explore shopping, decide it is not for them and never perform their first shop. There are a whole lot of folks who get started, do a few shops and quit. It is not and will likely never be a substitute for a "real" job because shopping is not a 9-5 with a steady paycheck and benefits such as sick days, vacation days, insurance, retirement plan, etc. If you feel uninspired you can't just show up at the office do a little something to get by for the day and get paid. You are paid by the job and each job puts you center stage. The majority of shoppers seem to do it for six months or less.
So the progression of shops from the basics to what you can find via Jobslinger is a sensible plan. Once you have made a decision that you DO like mystery shopping and it DOES work for you, that is the time to settle down with the list of companies and spend time signing up with large numbers of them.