Levinswap is an application on xDai that offers liquidity for the tokens you purchase. Levinswap offers the ability to instantly sell your assets, at the market rate. The price of the tokens on Levinswap fluctuates based on supply and demand, and total market liquidity in Levinswap. Uniswap is the same but on Ethereum.
SwapCat and AirSwap allow you to create sales announcements at the price of your choice, smart contracts guarantee the transaction between you and the buyer. As soon as a buyer is interested, he can interact with the smart contract to buy your tokens.
Be careful, if you want to buy on the secondary market (Levinswap, Uniswap, AirSwap, and SwapCat), you must be whitelisted for the relevant property.
You can also sell your tokens on the RealT website. Using the ‘Sell Tokens’ button found on the homepage you can generate a sale request. Sales through the RealT website take 8-14 days to process. The tokens are sold for the fair-market-value of the property, as determined by the most recent property appraisal. All properties receive new appraisals once-per-year.
With Levinswap/Uniswap, you are guaranteed to instantly be able to sell your tokens, however, the price you receive in the sale is determined by market at that time.
By selling on the website, you know the price you are selling the tokens for, but it is not an instantaneous process.