Of the companies I've worked with Bestmark is the fastest. They send checks though, which is a pain, but it is fast. I have $100 due to me from Goodwin Hospitality for shops I did in early July. I think they pay at the end of the next month you do the shop. They take a long time BUT they have the best shops IMO. Bestmark has pretty terrible shops, MOST of the time, but not always. I did do some pretty amazing shops a few years ago for a fantastic restaurant that was a $100 reimbursement. My husband and I did about 13 of these, which equates to about 1300 saved on dining out. That's pretty significant.
Digressing. Sorry. I did a car was shop for Goodwin on 6/14 and did not get paid until 9/19. However, the shopper history is very transparent and it's easy to see when you submitted versus when they paid. The car wash shops, I did 4 all took more than 2 months. Since it was a dump of a chain I figured it took them awhile to get payment from the client.
Shared Insight takes forever, but they never give me ANY hassles. I"ve done many shops, that are fairly easy, and the credit is always there the next day. As long as I see the credit, my nerves are calmed.
Secret Shopper also takes a long time to review the report, then a long time to pay, plus it's a check. I stopped shopping them a long time ago. Sometimes out of boredom I will do one, and instantly regret it. They are like those places that have coupons that are a great deal but you end up eating at the back of a warehouse. Secret Shopper shops are also the hardest to find, the most obscure, and the lowest paying. But, that was my first MSC so I didn't know better at the time.