Mystery Shopper

I have never done any mystery shopping before, but I signed up for one service called GAPbuster. So far so good. I got an email today that says I was accepted. I have to do an online orientation and then I can get assignments. I haven't done the orientation yet, so I haven't received any assignments but it looks like they do lots of McDonalds, Radioshacks, etc. This is just another way to get more extra income. I've heard both good and bad stories about mystery shopping, but not having experience with it, I thought I'd give it a try.