This is similar to house flipping, where a home is purchased and fixed up in order to sell for a fast profit. Unlike house flipping, however, there is essentially nothing to be done with the domain name in order to increase its value. Therefore, the key to a successful domain flip is being in the right place at the right time in order to acquire a valuable domain name before it is given a higher price.
Think of ways that the domains you buy would be a valuable asset to the buyer. Picture someone who would benefit from buying the domain in a space you are very familiar with. If this was you and someone was trying to sell you this name, would it be beneficial for you to own? Be honest. If so, why? If not, why? Use those answers to refine your search for names.
Your course of action really depends on how much work and effort you can put into the expired domain. If you're barely able to maintain and optimize your current site, you probably want to just 301 redirect the old site (note: see my amended comment above about the link value not likely to be passed). If, however, you're more creative and have some time on your hands, you can try your hand at crafting a microsite. If you really know your stuff and are experienced at making money off various websites, you'd probably do well with the third option. 

Do you want to learn how to make money buying and flipping domain names? If so, this guide will provide you with the basic knowledge and direction required to get started! Unlike domain name investing, where a "buy and hold" strategy is the standard technique, domain name flipping is all about finding valuable domains and quickly selling them for a profit.
That being said, many things have changed over the years. The days of MFA and quick flips are mostly gone. My advice to those new to domaining and wanting to give it a try is to take it slow, do your research, and if you do purchase a domain with the hope of turning a healthy profit - put some real time into it and build something useful. That way it's easier to monetize and easier to sell.
Perspective buyers are able to directly contact domain holders in cases where the desired domain is no longer available. Most registries openly publish the names and contact data of domain holders. Once this information is gained, buyers can get in touch with domain holders and make an offer for the name. Sales are also known to occur in instances where the original domain owner had no prior commercial ambitions
There are many different ways to buy and sell domain names. Many standard domain registrars, such as GoDaddy.com, will facilitate sales via auction. Meanwhile, specialized websites, such as Sedo, are designed exclusively to buy and sell domain names. Finally, parking domains with a for sale page is a great way to draw targeted interest from potential buyers.

1) pending delete auctions.  These are domains that were not renewed and are going through a pretty complicated drop process.  You can backorder these names at the auction venues and then each attempts to "catch" the dropping domain.  If one is successful you win the domain at $59 if you're the only one to backorder the name.  If more than one person backordered the domain a 3 day private auction is held.  Once the domain goes through the drop process, the back links have pretty much zero SEO benifit to the new domain owner.
In the grey hat SEO world, the thought is that you can take a domain that is keyword driven, do a quick optimization to get the site ranking, and sell it off at a profit. It could, and does happen daily. How much time is invested in optimizing a site to get to page one, vs how much the site will sell for? (remember that quote at the beginning of this article?). Let's put it into simple math:

Dictionary Word/Pronounceable/Memorable/Brandable: A dictionary word domain name is very valuable. Of course, the more popular and widely used the word is, the better. For example, “marketing.com”, “cars.com” and “hotels.com” are 7-8 figure domain names. Even if a domain name isn’t a dictionary word, being pronounceable and/or memorable and/or brandable are all big pluses that add to its value.
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