You are better off going to the new member area of this group and looking at the info for new mystery shoppers. No scammy stuff in there, just a boat load of information.
Start with Presto and IPSOS. Do a few small jobs to get the hang of it. From there just keep building and signing up with more companies. Try some different types of shops, find what you like. Reviewers will give feedback, learn from your mistakes. It gets easier but we all still mess up here and there.