I think most people would be OK with an additional flat fee so long as the notice is clear and conspicuous. For example, if I were renting a space daily and had to tack on a flat cleaning fee, I might write something like this:
$99 per day, plus $20 flat fee
In other words, you can develop whatever fee structure you want. You just have to adequately explain it to customers so they can make an informed decision.
$99 per day, plus $20 flat fee
In other words, you can develop whatever fee structure you want. You just have to adequately explain it to customers so they can make an informed decision.