They are scams, so the easiest thing to do is not look online.
Company's hire " secret shoppers" directly , as in their own employees, or through marketing companies. However with the economy the way it has been the past 3-4 years, nobody is doing that anymore.
As for work from home ideas, the only legitimate ones are either to be an employee of a real company, and see if they offer working from home vs. working in their office, or to start a business on your own, sell through Ebay. etc.
I do secret shopping for strategic reflections. I've worked for them since 2007. Be prepared to take some tests to qualify. Don't give out any info to any emails you may receive who say they will pay you to check out western union at wal mart. Wal mart does not have western union. You are never paid before you do a job. It takes 6 weeks for me to get a paycheck so it is not a get rich quick job. Depends on your location on how much shopping you can do. Good luck