Welcome to the forum! 'Good companies' is a very arbitrary notion that depends on what the individual shopper values. For example some like quick payment and are willing to take lower payments for the speed. Some are more interested in a larger fee, even if they need to wait for it. Some like large reimbursement shops, some prefer spending little out-of-pocket to be reimbursed later. And then you have the issue that not all companies have shops in all markets. So I would encourage you to look at the "Official List of Mystery Shopping Companies" that is at the bottom of each page of the forum. There you will find both links to register with legitimate companies and discussions about the company. As for certification, some companies may offer their own certifications for particular shops to show that you have read and understood what is expected of you. The MSPA also offers certifications for which you pay, but which are not necessary for you to do shops.