Apologize if this is common knowledge. The email below was a pleasant surprise to me, so I thought I'd share. I inquired about selling my timeshare to see what help each company tells their owners. I wish the other timeshare companies I contacted were as honest and helpful as Marriott. 
Here is part of the email:
"As promised, here are the websites that might help you to sell on the external market. If you have any questions, do not hesitate to give us a call. Please be advised that Marriott Vacation Club does not endorse any specific resale company.
We have been told by owners that the information provided by The American Resort Development Association (ARDA) www.arda.org/resales and the Timeshare User Group (TUG) www.tug2.net is of particular help when evaluating the current resale market and available selling options. One helpful article in the latter is "learn how to sell your timeshare- free advice,
Keep in mind that ARDA’s advice is from the perspective of a professional trade group while TUG’s recommendations often come directly from timeshare owners.
To understand how to price a property to market demand, owners often rely on licensed real estate brokers or the information provided by websites like www.redweek.com and www.myresortnetwork.com.” Choose the option to buy a timeshare and select the type of ownership you have so you are able to see how much other owners are selling your type of unit for. Then if you decide to do so, you may create an account and post your week for sell.
You may also go to www.ltrba.com, which is an independent, non-profit association created by licensed timeshare professionals to provide a trusted and transparent marketplace for buyers and sellers of resale timeshare interests. Once you visit the site, you may click on Member Directory for a complete list of participating agents."
Here is part of the email:
"As promised, here are the websites that might help you to sell on the external market. If you have any questions, do not hesitate to give us a call. Please be advised that Marriott Vacation Club does not endorse any specific resale company.
We have been told by owners that the information provided by The American Resort Development Association (ARDA) www.arda.org/resales and the Timeshare User Group (TUG) www.tug2.net is of particular help when evaluating the current resale market and available selling options. One helpful article in the latter is "learn how to sell your timeshare- free advice,
Keep in mind that ARDA’s advice is from the perspective of a professional trade group while TUG’s recommendations often come directly from timeshare owners.
To understand how to price a property to market demand, owners often rely on licensed real estate brokers or the information provided by websites like www.redweek.com and www.myresortnetwork.com.” Choose the option to buy a timeshare and select the type of ownership you have so you are able to see how much other owners are selling your type of unit for. Then if you decide to do so, you may create an account and post your week for sell.
You may also go to www.ltrba.com, which is an independent, non-profit association created by licensed timeshare professionals to provide a trusted and transparent marketplace for buyers and sellers of resale timeshare interests. Once you visit the site, you may click on Member Directory for a complete list of participating agents."
