I think it depends. Some MSCs offer no payment on shops that are very popular, figuring that if enough shoppers will accept the shops for reimbursement only, then why pay a fee in addition to the reimbursement?
There are some MSCs that just do not pay fees for the most part. A Closer Look comes to mind. I will do a shop (restaurant shops are my favorites) for no pay and reimbursement only, BUT, to be attractive to me, the reimbursement must cover the cost of the ordering requirements and I must like the food and the location. Otherwise, why? Although A Closer Look has some shops I really like and the reimbursement is generous, so I happily do those shops, they have others with reimbursements that do not pay for the required items. I find myself doing fewer and fewer ACL shops because of that. In addition to no pay and low reimbursements on some shops (mostly fast casuals), they require recorded phone calls on some shops and an increasing number of shops require photographs. I saw one today and laughed out loud - the cost of the required items to be ordered exceed the reimbursement, there is no pay, and they require photos of inside, outside, all food items, and BOTH bathrooms - so I must send my guest into the restroom to take a photo. I was laughing as I deleted the e-mail for that one.