Dandy, the following is what I recall, but, at 78, I could easily be in error.
Corporate Risk Solutions, like other companies, decided to rack in some mystery shopping money and formed a division for that purpose. At some point, I do not remember when, Custom replaced Corporate in their title. Until your post, I was unaware of the last name change. The MSC, under whatever name, holds the record with me for the fastest payment at approximately 25 minutes; a $50 fee and $124 reimbursement. Excluding that shop, their average payout was seven days.