Take your normal social worker resume. Bring it up to date with "Independent Contractor - Mystery Shopper" with the dates you have been shopping (5/6/2015-present). I don't know what format you use for your regular resume, but I have a little blurb specifically about what I was doing, so for example 'Performed over 300 shops for 9 different companies including bank, restaurant, telephone, hotel, automotive and cell phone shops. Reported on the three major platforms and proprietary platforms.' I would then edit down the blurbs on other former positions leaving mostly skills that would be relevant to computer skills, phone skills and scheduling. A social work background would normally include people skills that would be needed to be a scheduler, availability and responsiveness to clients (shoppers and MSPs), non-judgmental and calm in crisis.