RULE #1 - DO NOT PAY A MYSTERY SHOP COMPANY FOR SHOPS!!!!!!
I have used their directory to sign with other companies.
They hounded me for ever and gave up. Then recently they sent me another email to give in to their 'bargain' rate.
RULE #2 - ALWAYS FOLLOW RULE #1!!!
There are plenty of Mystery Shop Co. out there. Sometimes they are related to each other and will tell you to check their sister site.
Another suggestion is MSPA. They list a lot of reputable companies and you do not need to be Gold Certified. I am not certified at all and still get a lot of shoops from these companies.