If you have to collect it, collect it. Do you have a sales tax # ? Here in tennessee, I have to collect it for mulch, topsoil, etc, but not for delivery of said materials, or for mowing. Itemize it, and point out the positive. Tell them, no tax on delivery, so you are saving them money!
Don't argue, stay positive, and make money!
My wife and I have also run a sucessful business at flea markets (Different product) and people don't expect to pay tax. Sales tax is high here (9.75 %) so they get a little huffy about it sometimes. At ths time, we have to figure out if we want to pay their tax for them to save the sale, so that's handled on a case by case basis. Sometimes ya got wiggle room on a price, sometimes ya don't.
Wording is everything. Remember, and tell them if you have to, smiling, not nasty, that you are NOT charging tax, the state is, you are working for the state...collecting taxes, remitting the funds to the state, and taking complaints. Ad for this, they ARE NOT paying you. The last 2 parts about taking complaints, and not getting paid for it, ya gotta be careful with. Some folks have no sence of humor, and you'll get a rep as a pr!ck.
Sometimes, all ya gotta say is, "I don't like paying taxes either, but we have to. We're a real business." You don't have to point out, the fact that the ones who don't collect taxes get a shocker at the end ofthe year.