The Client IS Always Right (Wrong)
Do you work for yourself or your client?
What a client wants is not necessarily the correct plan of action, you know their plans are wrong, so do you follow their instructions regardless, even though you know their leaflet campaign will fail, or do you point out the problems?
In some cases clients have utter belief that they know what will work and do not expect you, the lowly leaflet distributor, to have a different opinion. Of course, when they do not receive any response, it will be your fault :)
The importance with this is you know the area that has already been blanketed by x industry. You also know which areas have not been touched so makes an ideal opportunity for approaching clients with “x area hasn't had your industry deliver for over a month, I suggest you consider having x amount of leaflets delivered as soon as possible”.
You have a potential client asking for the same area only two days after their competition has delivered. The householder has already made the decision of whether they would like the services of that industry so cutting down the potential of a response from your client by a huge amount.