As you know mystery shopping is a method to gauge the real customer experience. The idea is to get the right feedback on shopping experience through a mystery shopper. The person who is doing the mystery shopping can keep the product after giving the feedback to the company. In some cases companies also pay money to the shopper. There are some scam sites that ask you to register by paying a fee so that companies can select you for mystery shopping. But the fact is that genuine mystery shopping opportunities are free on net. Once you pay any fee you are not going to hear from them again.