Charging for three 7" plowings is pretty darn fair if you ask me. 21" = don't leave your house without a 4X4 and a lot of back breaking shoveling.
The customer has to understand that it is entirely weather related and you do not dictate the storm but rather it dictates the level of service required. Also your time and the wear and tear on your equipment is worth every penny you charge.
Keeping a customer is one thing but this is after all a busines not a charity.
Try paying someone to shovel that much snow and you let them get of cheaply.
Its all in how you market it to them in the contract phase.
I do all residential and have never had a problem getting paid.
in my contract I clearly state that the cost for the driveway will be
I also clearly state that additional visits to the site in an extended storm will be charged out at $xx.00 per each additional visit.
They might call and question during the summer before they sign, but they sign the contract after I explain to them the logic of plowing smaller amounts of snow several times, than say 21 inches all at once.
I can see them complaining if you say in your contract that you will charge them $35.00 to plow their driveway each storm then hit them with a $105.00 bill for the first storm.
In my contracts I include a terms and conditions page that outlines how the work will be approached and performed.
This usually clarifies any misunderstandings. If a customer has questions they are usually addressed before the contract is signed.
I just gave up my driveways this year and went to all parking lots.. the way I charged was if I got $40 to plow and I had to do it twice I would charge $40 again if and I mean if I had to go a third time it was $0 for the third time. The way I see it is in ten years of driveway I probibly only had to plow all my drives 3 times during 3 storms other than that I had to do some of the first drives on my route a 3rd time because of my schedule not the storms demand... but there were lots more times that I got paid the $80 for two pushes that other people would only charge $60. All my customers seemed to understand that I do plow the same area each time I show up and should be paid the same.
If my customer called me because they had 1" of snow and wanted it cleared they got charged full price no matter how many times I had been out.