I try to honor their request. Rotations are established for a reason--to make the shopper less of an identifiable, familiar face. At the same time, sometimes I shop a location with the store itself as the client, sometimes with the 'landlord' as the client, sometimes with a specific product as the client. You just have to use good judgment as to whether your presence would be noted.
An example: There are 3 shops out there right now with 3 different companies for my branch of my bank. One is a 'new customer' on behalf of the bank which obviously I can't do as this is already my bank. One is a competitor, which I certainly can do. One is on behalf of a credit card company, which I also can do. In reality, I would not have an issue with doing the competitor and credit card company shops on a single visit as the client is different, as is the vast bulk of the information collected.
There is a 'dinner at the bar' shop at a local restaurant by Company A. There is a 'dinner in the dining room' shop by Company B. Company B requires you have not shopped the location for 90 days. For us, this is reasonable as it is a restaurant we go to only on shops and the place is not huge, nor is there high staff turnover. The client in both cases is the restaurant. We prefer the dinner in the dining room so do not do the shops for Company A.
Take a department store. A watch company may have you shop the jewelry counter. A shoe company may have you shop the shoe department. A credit card company may have you looking for promotional signage and make a purchase or a purchase with return to see if the cashier offers you the card. There may be other specific clients and there might even be the department store itself shopping itself. If the watch company shop specifies I cannot have shopped the location for 90 days I will assume they meant the jewelry counter and go ahead and take the shoe or credit card or other shop that does not put me at the jewelry counter.