Did you have this lawn last season too? If so, what has changed? Customer expectations, environmental or weather conditions, your program?
It has been exceptionally rainy in your part of the country, right?
Consider having soil tested for this yard and for a similar one where you and the customer are both happy. See how they compare. There maybe something you can tweak. Often changing what you apply for one of the micro-nutrients can make a difference of the type your customer demands. Try to make sure you are comparing similar species and cultivar from one lawn to the next. Often this information is unavailable later but try. In terms of discussing it intelligently with the customer, let home know you are bringing a little more science into the care of his yard and will find an answer.
Photos will be a help to everyone here interested in trying to help you.