While washing a car at a customer's house, I was stopped by an older gentleman next door and asked why I was not using a sponge, because "those wash mitts are terrible for paint."
After taking the time to explain to him that sponges hold dirt at the surface and can scratch the clear, mitts absorb and release dirt much more easily (especially with a two bucket method) and are gentler to use, not to mention softer, he simply replied "just can't tell you young guys anything anymore. Just don't mess up that car."
To which I replied "yes sir" with a smile. Some people just don't get it. I live in a well-to-do area that has a nice sized car wash which sponsors the local middle and high school sports teams. They drive your car through an automated (non-touch free) car wash, and when it comes out five to ten guys are waiting to wipe down these cars with the same towels they've had on their shoulders all day. I try to get the word out about my business at local car get-togethers and can't believe how many blind supporters they have when there is a better product just begging to be had.
I've been laughed at when a local police officer asked me how much to polish his disgusting patrol car.
Sorry for being so long-winded about the subject but people do get what they pay for. Unfortunately, not everyone will see the difference in the work we do vs. the gas station car wash. Plain and simple. Your customers love you because they can see it, and will tell everyone about you to whomever they know who would be able to see it as well.
I think your reply was fairly straight forward and courteous and professional. Question is, does the person you replied to even know what "paint beading," "clay bar," "sealant," or a two bucket method is in the first place?