Sights on Service pays reasonably quickly. Little contact with human beings there, but that is fine with me! I am able to get my cat's regular yearly exam free each year, which saves a ton. The health club shop I only warn about because you will get pounded with follow up calls from them for months!
This company used to do shops for a major restaurant chain that reimbursed more food than a human family could consume in a meal. We would dine and bring home the next day's lunch (and sometimes even dinner) in a box. I miss those!
I only have done one shop for Goodwin. I had to remind them to pay me, but did eventually get paid. Because of that, I've avoided them.