The wood is supersaturated with chemicals and over then next couple of months it will continue to off-gas.  

You are technically required to be licensed to spray chemicals.  

Is there a difference in how often this is required with ozone vs chemicals?

Guest will leave trash in it and around it, needs attention to the water level and chemical balance, cleaning of the filter every couple days if it's being used alot....much more sensitive than a pool.

The chemicals/treatment will not likely be done correctly if you are depending on your cleaners or a weekly service (they are dump and run for the most part).

Then if someone came down with something due to chemicals being wrong they take on the liabilty for that.

They have dogs so they claim that they don’t want the chemicals.

So here goes:Taking into account the basic function of a car wash, manned or un-manned, you have a considerable amount of moving parts and tremendous amounts of water and chemical treatments.

my recommendation would be porcelain wood-look tile with chemical grout (Never seal, no stain) in the whole house.

People are afraid of what they don't know, in some areas people don't want city water because it comes with the city price tag and chemical taste/smell, in other they're afraid of what is in the water and what could go wrong because they're used to the city water.