Here's an old post on search engine roundtable that claims google's policy is to discount previous backlink juice when a domain changes ownership.  I'm not convinced whether this is actually true or something Google says to discourage excessive domain buying / 301 redirecting for SEO benefit.  The comments above seem to give varying opinions on this matter. Would be great to get to the bottom of that one!
Many individuals have the habit of collecting attractive domain names but never using them. If so, why not get rid of unused domain names and in the process, make some cash? It is important to understand the whole process of selling domain names. On the outside, the process may look very easy, but unless a trader is well aware of how the whole process works, it is not easy to find a buyer.

Your domain name registrar may provide you with a free one-page Website tool, which you can use to create a “this domain is for sale” landing page. Alternatively, you can create a single page (perhaps a hidden page hanging off one of your existing websites) that indicates that your domain names are for sale. You can then forward all of your domain names that are for sale to that one page.
Buying and selling domain names is an exciting adventure that for some seems to conjure up images of finding hidden pirate treasure or guessing the winning combination on the next Powerball. Stories abound of domains that were purchased for $8 dollars 15 years ago being sold today for millions. Of course, that leads the more adventurous of us to wonder, “How can I do that?”
The easiest and least time consuming option is to 301 redirect the old domain to your existing site. This tactic obviously works best if both sites are in the same sector and are targeting the same keywords; otherwise, if you have a pet supply site and you buy an old Texas Hold 'Em poker site, a redirect probably might raise some eyebrows among the search engines. If, however, your site is brandnamepets.com and you buy onlinepetsupply.com and 301 redirect the domain over, you're inheriting a lot of topical and appropriate links.
Also, Sedo.com, makes millions a week selling domains,even in the past week[3]! If you want to sell here, I would probably use a paid category or featured listings, one of my category listings, got 44 views in just 1 week but still waiting for a sale this month, hopefully. I would not really on this as a business, unless you add web development to it, and also, be sure to check that you are making a good profit, say within 6 months!
Flipping domains are similar to flipping houses in real estate: You buy a property with potential, improve it, and then sell quickly for twice the profit (or more). Between 2005 and 2012, internet marketers had been obsessed with flipping domains… and for good reason. Many were successful at buying plain old domain names, spicing them up with keyword-stuffed content, giving them much-needed traffic, and then selling them off to the highest bidder. But in 2017, can this still be a viable online business?

Selling on auction sites is another great way to find buyers. Ebay.com is perhaps, the most popular place to sell domain names. Afternic.com is another site that allows sellers to find good buyers. If you have premium domain names, become a member at GreatDomains.com and list your domain name there. The site is a reputed marketplace and brokers deal with thousands of dollars trading domain names. You can also sell domain names through Sedo.com, a site which has its own selling program. Sedo.com has the largest marketplace in the world, and boasts of having a list of the most expensive domain names in the market. It also has a safe and secure escrow service for domain name buyers and sellers.
Here’s what you DON’T want to do: Target prospective buyers based on their perceived economic status, without any insight into the industry you’re targeting. “Lawyers seem to do well,” you think, “maybe I should start selling names to them.” So you rush out and buy a bunch of domain names you think would appeal to the law firms you’ve identified as potential buyers. Without knowledge of the space, you may not know that the American Bar Association and other industry-specific organizations set rules that govern some aspects of legal advertising. You’re not going to strike gold selling names your target buyers can’t use.

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.
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