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!

Be careful! When searching for domains, it might be tempting to, for instance, buy (if it were available) and then try to sell it to McDonald's. The logic here would be that they own the .com and wouldn’t want anyone to own the .net and use their name, right? Also, it’s a big name so there’s gotta be a biiiiiiig payday comin’, RIGHT? Wrong, and wrong.
To join, you’ll need to purchase an annual GoDaddy Auctions membership for $4.99 a year. Once you’ve purchased a membership, you can take advantage of member benefits such as our Auctions Tools, which can help you prepare before buying or selling any domains. After joining the auction community, you’ll quickly learn how to navigate the world of domain buying and selling and can begin to make money by investing in domain names.
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.