ResortGems.com is legit - I'm one of the founders. We were founded in 2009, have belonged to ARDA and have a strong BBB rating - noted on our site. You may not have heard of us because we're relatively new. Our model is to rent timeshares online. No cost to owners to list and we take a 15% fee if and only if we find a rental. Owners establish the net price they want - for example, if you need $1700, price it at $2000 and post on ResortGems. If we arrange the rental, you get your $1700, upfront.
When we find renters who need a place that we don't have, we sometimes reach out to owners on Redweek and others to see if they'll rent to our customers. That's how Chuck was contacted. If a unit is available we arrange the transaction on behalf of our customer, collect the rental fee and pay the owner - in advance of the rental taking place.
I hope this answers the question raised