2nd post, 2nd thought.
before you drive all that way, test some different products in a customers or neighbours drive for free!
Tell them, free cleaning to test some products in a small area. Then when they like the results give them a discount on the rest of the drive, really good discount.
Now go the 40min drive to the original customers, armed with best products and best knowledge on how to do the job.
ps. my neighbours and customers love that I do that for them sometimes, even had one ask me recently if I needed to come and do some more tests on his property!
This fellow watches what I do, gives some good pointers sometimes, and laughs and laughs with the ease of the results versus how he might clean them himself with a garden hose and brush.
ps, I also get Tea or Coffee when he is around