Hello and welcome to the forum. The only way I've been able to find work is by signing up with companies who have the jobs. The more companies I sign up with, the more jobs I see. Some companies will have work in your area and some won't, but that doesn't mean the situation will stay the same. Companies pick up new clients and lose the old ones with regularity, so it's a good idea to sign up with everyone. If a company picks up new work in your area, you'll be ready to go.
Regarding financial security, I haven't run into any problems with the companies I've worked with. Some of them pay by company check, some deposit into my personal bank account, and some deposit into my PayPal account. It all seems to work. You can set up a separate account for your business but you may not be able to get a free account. Lots of banks offer free personal accounts now.
I don't know of any source that will list work from all companies in a geographic area. There are many, many companies who have work in certain areas but not nationwide. There are other companies who may have work in your area because they are so large. Some of those are Market Force, Corporate Research International (Cori or CRI), Maritz, and Bare. If you are in my area, which is DFW and North Central Texas, all four of those companies offer a considerable amount of work but you will have to share with a large number of shoppers. There is a link at the bottom of the page to a list of mystery shopping companies. That's a good place to start.
Since you are new, I want to caution you that no reputable company will pay you in advance. You will be paid and reimbursed as set out in the guidelines after your report is accepted. The average shop will be between $7 and $15.
Best of luck to you with your new business.
Mary Davis Nowell. Based close to Fort Worth. Shopping Interstate 20 east and west, Interstate 35 north and south.