Check the tax rules for your location.
In Washington State, you are required to pay sales tax unless you're a middleman, and then you're required to collect the tax from the end user. Anything we buy "tax free" has to have a "use tax" paid, in exactly the same amount as the sales tax.
They cracked down on carpet cleaners a few years ago, as they realized cleaners were going out of state to buy truckmounts or mail ordering most of their supplies from places that didn't charge tax. A lot of guys ended up paying hefty fines.