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!
Expired domains are especially attractive due to key SEO factors that are primarily associated with an existing backlink profile. If you are considering buying an expired domain, you can determine the quality of it by looking at the inbound links. When it comes to assessing the value of an expired domain relevant keywords contained in the second-level domain, a possible reference to products, brands, or services are all useful.
Many top-level domains, or TLDs, out there have the potential of being sold at top dollar rates. Gone are the days when domain names with ‘.COM’, ‘.ORG’ and ‘.NET’ were known as top-level domains. Newer domain names with ‘.US’ and ‘.IO’ are also worth their weight in gold. All you have to do is conduct thorough research in order to find all the good domain names you can park.
If you’re serious about domain flipping, one of the best strategies is to buy expiring domains that auctioned on the market such as GoDaddy Auctions. Make sure you pick domain names that have good traffic, backlinks and SEO metrics, or domains with the generic niche. Expiring domains with a potential for profit can be found using BuycomDomain.com, this is a free website/tool that helps you sort through the domains by different metrics (age, traffic, backlinks, domain authority etc).
When speaking about an expired domain’s backlink profile, this refers to the incoming links that have built up from when the domain was previously in use. Recently-expired domains that have long histories aren’t unheard of. While the pre-existing content of the domain rarely remains visible when the domain is re-registered, links on the other hand do remain, as long as the new owner doesn’t devalue or delete them.
Unfortunately, most domain names take at least a couple of months to sell, especially without an attached website. Thus, there is no need to become discouraged if your domain name does not sell immediately. Most people make the mistake of quitting their domain speculation endeavor after waiting for several months to sell without success. In reality, domain name squatting can be just as profitable, and it is a valid form of long term investing.
The domain name industry is quite similar to the real estate industry in a lot of aspects. There are end users, brokers, consultants and domain flippers or “domainers”. Domain flipping works similarly to buying a house, renovating it (or even sometimes just sitting on it) and then selling it again at a higher price point. The gist of it is: you’re purchasing a domain name and betting it’s worth (or will be worth) more than you paid for it. If you’re right, you get a nice paycheck and move on. Those who make a living out of this just rinse, repeat, and scale.