The other issue with a dull mower blade is that when the grass is injured and shredded it becomes extremely vulnerable to plant disease.  Almost one hundred percent of the time you will find leaf spot on a lawn that has been mowed with a dull mower blade.  

Finally, when a customer asks you if they should bag or mulch their clippings you should always tell them to mulch them if possible.  By returning the grass clippings to the soil they will be helping to keep much of the nutrients provided by fertilizing in the lawns system.  Research has shown that mulching the clippings could add as much as 1 lb of N. per 1,000 square feet annually.  Tell your customer that there may be a time when bagging the clippings is more appropriate but you will inform them when that time comes.

Sometimes working with your customer to teach them the perfect methods of mowing can be difficult.  Mowing the lawn is a chore and many customers don’t think about how important it is to having a nice lawn.  Very few homeowners are able to maintain a perfect mowing regimen and every time something is done outside of perfection there is a blemish created in the lawn that we must contend with.  Do not ever get adversarial with a customer about their mowing habits but always make a concerted effort to help them understand that mowing properly can have a huge impact on turf grass quality.