First, I would not sign up for any company that asks for money.
Second, all reputable companies are listed in one (or more) of these three places:
MSPA website: [
www.mspa-na.org]
The link at the bottom of this page
Volition website: [
www.volition.com]
Third, many/most/all of the reputable companies are members of the Better Business Bureau and proudly display it on their pages.
I am fairly new as well 3 months) and by simply making sure each company is listed on one of the above three locations, I have yet to be ripped off with approaching 200 shops. Do be careful: each company has its own rules and guidelines and, if you don't follow them, they could refuse to pay you. However, I have not had that happen as of yet. Also, each company has its own pay schedule: Sometimes you'll be paid in less than two weeks. Sometimes it takes three or four months.
Good luck. It's fun.
Hard work builds character and homework is good for your soul.