How Can I Sell My Credit For My Vacation Condo In Cancun

I have a rental Credit With An owner in Cancun for a beach side two bedroom condo.

After Talking with Them, They Have Agreed to give me a credit and Gave me permission to sell it so I CAN get my money back.I WAS going to list it on du site Originally I got it from (cyberrentals, homeaway.com) goal Costs 80 bucks it for 3 months.

Does anybody know of "any good sites That I Can we post this information so I Can sell this in time for Christmas Some money for the Family.