Absolutely correct, Pam or (Cujo).
I would like to add that even if you clean EIFS correctly, you may still have problems with the customer. You must be aware of the underlying issues/lawsuits regarding EIFS. Older buildings have MANY problems with moisture condensing and/or dripping behind the siding, soaking the framing. Wet wood rots and attracts termites. Wet wood voids ALL termite warranties. (I know, 6 years as a manager for Terminix.) Newer buildings have re-designed EIFS, which is less likely to allow moisture to condense, but may still allow water to penetrate if not properly caulked.
The customer should be well aware of these issues, but if they think you are not, they may try to include you in their frantic legal battle to pay for damages - which can run into the tens of thousands and more. (Just think, removing and replacing all of the siding and framing on an existing structure!)
Something in writing wouldn't be a bad idea.