The emoluments clause, also called the foreign emoluments clause, is a provision of the U.S. Constitution (Article I, Section 9, Paragraph 8) that generally prohibits federal officeholders from receiving any gift, payment, or other thing of value from a foreign state or its rulers, officers, or representatives.
Thing is. You can't prove (it's very difficult to prove) people buying out entire floors of Trump hotels and buying lifetime memberships to maralago are doing so as a gift/payment to Trump.
It's a business. It makes money. As it's written, there nothing in the emoluments clause prohibiting the ownership of private businesses. It just prohibits receiving of gifts. Which, I assume, must be directly given to the President.
However, it does go on to say:
The plain purpose of the foreign emoluments clause was to ensure that the country's leaders would not be improperly influenced, even unconsciously, through gift giving, then a common and generally corrupt practice among European rulers and diplomats. An early version of the clause, modeled on a rule adopted by the Dutch Republic in 1651 that forbade its foreign ministers from receiving "any presents, directly or indirectly, in any manner or way whatever," was incorporated into the Articles of Confederation (1781)
So. Apparently if you can show payments were intended to indirectly bribe Trump. Then perhaps there's a case to be made.
Personally. I'd say it's obvious people are buying favor with Trump.
But I can't prove it. Apparently neither can the people trying to sue Trump.