A frequent advert on my Yahoo Mail page is for "Mystery Shoppers" for grocery stores. The reason I remember it (and appreciate it) is because it features (what I believe to be) a STUNNINGLY attractive redhead.
While certainly enticing (eliciting mental questions like "Do the other mystery shoppers look like her?" and "If I sign up, is there any chance of going to group meetings?"), it's hardly practical.
Mystery shoppers are supposed to blend in. They are used (at least in the grocery business) to check for proper customer service and item pricing.
If you use an amazingly attractive woman as a mystery shopper, your check of canned corn prices may be useful, but I guarantee you will get a skewed sample regarding customer service.
Why? Because every male employee in the store will not only bend over backwards to help her in any way imaginable (if only for the chance that she will say three words to them), but they will also call up friends in other departments to tell them about her, so that they will try to get a look and perhaps "help her" as well.
Sad fact of human nature (and male attitudes).
That said, if mystery shoppers DID start looking like this particular example, I may just return to the grocery business.