Welcome. If you are just starting out, go to the New Mystery Shoppers section here and read everything you can. Then proceed on to the other sections and read more. There is a ton of free information covering about everything under the sun for shoppers here, and you can save yourself some hassles and learn alot by going through it all. Sign up with Jobslinger.com to get an idea who has shops in your locality. It's free.
Oh, and never pay to shop - books, conferences, certifications, job aggregation services? You don't need them to start shopping. Once you decide if you are good at it, if it fits into your lifestyle, and if you like it, then you can decide whether you want to spend the hard-earned cash on things like these. Until then, and after, really, the information is free on the net.
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“Lying in bed would be an altogether perfect and supreme experience if only one had a colored pencil long enough to draw on the ceiling."
~Gilbert K. Chesterton