You need to check with the social security office to make sure.
But, I think you can earn $3000.00 a year before it affects your benefits.
You will only get a 1099 form from mystery shops when you earn $600.00 from them.
So move around a bit between the companies and don't make that much from one and then you don't have to file income taxes. if you don't get any 1099's.