I have shopped for them and their behavior on shop assignments was about standard for requested shops. Not specific to Service Sleuth, my sense is that the job is assigned to a shopper and a fair number of other folks are left in "pending" to use as backups in case the assigned shopper flakes or fails to perform. I note on my job sheet what jobs I put in a request for and if I have not heard by a reasonable time before the shop, I cancel my request. Similarly if I find other jobs I will take them and cancel my request because when I request a shop it is to DO it--not to be a BACKUP.
Service Sleuth has been okay to work with. They have screwed up a couple of times but mostly been cooperative in getting things straightened out. When I have reported to them 'odd' or 'unsavory' issues from the shop site, my sense is that the information HAS been transmitted along to the client.
My only real issue with Service Sleuth is the extremely long pay cycle. They are making 'timely payments' at 3 months! (From their website "Payments are submitted to PayPal approximately 60 days after the last day of the month in which the shop was completed. Please note that it then takes PayPal up to 5 business days to process this transaction and clear the money for disbursement."
This makes it very unattractive to lay out cash on their behalf for reimbursement--though I have never NOT been reimbursed.
For those who are sensitive about such things, most of their editors love my reports and 10/10s are standard. They do have a couple of editors who seem incapable of awarding more than 8/10 and the comment "Some edits were made to clarify some of the comments." is a little bizarre when they neither contacted you for clarification nor have given you any notion of the nature of the problem.