By "white pad" I mean a white 3M Doodlebug pad which is the standard hull cleaning tool here in California. Here is a pic (holder on left has no pad attached):
I'm sorry, but your argument that a metal scraper is less damaging than a pad just doesn't hold water (no pun intended). And while I do not dispute that you experience extreme fouling conditions in your area, that doesn't mean that a scraper is the best tool for the job. Bottoms should never be allowed to get so foul that a scraper is required. Don't get me wrong, I take a scraper into the water with me every boat I dive. But only for removing three-dimensional growth, not as a general cleaning tool on anti fouling paint in good condition.
Here's my opinion; part of our job as hull cleaners is to educate the (frequently ignorant) boat owner about proper boat maintenance. And by "proper boat maintenance", in this instance I mean cleaning the bottom as gently as possible. If your customers think that letting their boats get so foul that they can only be cleaned with a metal blade constitutes proper maintenance, then you have an excellent opportunity to illuminate all the reasons that is not so. You are the professional here, not him. You speak with the authority that nobody else has. And once you have shown him why letting his bottom get anything more than lightly foul is bad for the environment, reduces boat performance and costs him money (lots of it, in the long run), he will understand why having you clean the bottom more frequently is a good thing and will save him dollars. On your end, your work will be easier and you'll make more money to boot.
I know that the prospect of moving clients to a more frequent schedule is daunting, but I have done it with a lot of success and using my method, once the customer sees the reality, going to a more frequent cleaning schedule is almost a no-brainer. I'll post more about what I do if anybody is interested.