I did mystery shopping for about a year before returning to a full time job. TrendSource is a legit company. A word of advice though, it is really hard to make any significant income mystery shopping, please don't get your hopes up too high. There are other companies where you'll "shop" for services and you'll have to spend money up front for that service, with payment coming 8-12 weeks later. If you don't mind being out the money in the meantime, you can get oil changes, hotel rooms, even salon services for "free".
If you are looking for part time work that you can set your own hours with you may want to consider a merchandising job. Good luck!