There's also Concierge Realty, a highly reputable and honest group... Just Google them.
They typically handle higher-end Marriott resorts (and many other brands, homes, etc), and have a good client base for whom they find accommodations.
Any of the agents can help. I've rented twice through them, and used Heidi Rustin (awesome) and Michelle Donato (fantastic).
You give them your bottom-line request, and they add whatever % they usually do----doesn't matter really because they don't take anything from your bottom line or net.
(Note: Recently they discovered that, because of their awesome reputation, others have pretended to be associated with them, and perpetrated scams, but Concierge lists each and every agent online so that you can rest assured you're dealing with a true and honest agent. They are truly an outstanding company, worthy of trust.)