If you are looking to sell a domain name that is no longer of use to you, a possibility would be to lease it through a third-party company such as Godaddy, which lists tens of thousands of names. If the name is a quality one, there are also premium agents such as MediaOptions, which deals with more selective domain names. An alternative option would be to lease it out on platforms such as Nameforest.com. Doing so will save you the time of having to find potential buyers, and will guarantee a higher success rate than attempting to look for a purchaser on your own.
There’s an important distinction to make here between domain flipping and website flipping. The latter mainly refers to buying and selling full websites. By full websites, I mean websites that actually have content and more often than not have traffic and revenue. When buying and selling websites, the domain name matters less as the main value there is the content, traffic, revenue, history/reputation, sustainability and growth opportunities. The same can’t be said for domain names where you’re just selling “the name” and hence it’s all that really matters.