No paperwork, no lawyers, not even an agreement from the hotel's actual owner, who is not in fact the lowly shift manager. Write down an arbitrarily big enough number, and the rules don't apply to you. He did it again in Justice League, buying a bank so that Clark Kent's mom could keep her house (it seems like he could have just bought the house?), and again on the Gotham TV show, buying a nightclub so he and his friends could enter. Again, no deals inked, no contracts signed, no attempt to pay off the bouncer who would almost certainly look the other way for, like, 20 bucks.
In Inception, Saito buys an entire airline solely so the gang can have a bit of privacy in the first-class cabin of a 747. A transcontinental travel service was successfully bought up in the span of what seems to be a week, when merely getting a lawyer to commit to a lunch order takes about six days.