However, I'd argue that most people in the business really struggle as they don't understand what makes a good domain name and what's a bad domain name. While I do not work in this field full-time, I can say that I can make a living of it, but it's probably because I don't ask for absurd prices (e.g. randomword247.com domain name for $8000 is just unrealistic and won't happen) and therefore can sell domains easier. 
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.
If you buy a dropped domain from Snap or Namejet, the backlinks seem to be worthless for SEO.  They are valuable for traffic if it's targeted to your site.  Go ahead and 301 redirect into your site because it's the traffic from the back links that is worth something.  I use the Google URL builder to redirect these names so you can see the domain the traffic is coming from.
Check backlink profile: If you’re not familiar with what backlinks are, they’re basically any public website that “links” to the domain in question. Since there are numerous shady tactics in the SEO world, expired domains’ backlink profiles should be examined carefully. Check if too many links are coming from the same domain or if links have weird anchor texts/use foreign languages. You can use a tool such as ahrefs for these purposes.
Be careful! When searching for domains, it might be tempting to, for instance, buy mcdonalds.net (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.
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.

While numbers like those above are impressive, most domains sell for significantly less extravagant prices and are generally in the two or three-digit range. Not long ago, those who were able to secure general terms (like icecream.com or pizza.com) not protected by trademark rights often found themselves sitting on virtual gold mines. The glory days of this boom have long since passed, and those looking for a profit in today’s market needto have a keen sense for coming trends.
If you’re patient enough, you can discover at least four to five very good .COM domain names at attractive prices. However, you’ll need to carry out some research and find out the right places where they may be available. I’ve seen that such .COM deals can also be bagged from popular domain marketplaces like Flippa.com, or from the private portfolio portals of sellers, provided you employ the right strategies. You can contact the domain owners directly too. There’s no harm in emailing them directly to negotiate the prices.
Sometimes people purchase domains that they plan to build a website on or sell in the future, but it just doesn’t end up happening. If an individual decides that it is no longer worth the yearly investment of keeping the domain in their account, they may choose to let it expire. Or, someone might just forget to renew the domain before the expiration date. If this happens, it’s a great chance for other domain investors to score rare domain names that are pending delete. Spending time perusing the list of recently dropped domains can be a worthwhile way to find high quality domains.
I have an interesting twist on how I have done it in the past. I will buy a domain and use it as a development domain for blog posts and things of that nature. Then over time it will gain DA and PR. Then I will sell it off and buy another development domain and start the process over. Not quite the process you mentioned, but it works. People will link to the development site to show things off as well  sometimes, so that helps.
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.
Finally, you want to head over to domaintools.com. Then put the domain into here. What this will do is it’ll show you the history of the domain, because a lot of times these domains have been dropped like four or five times and a lot of people in SEO feel this way. I’m not sure about it. If a domain has been dropped several times, then Google does actually devalue the links pointing to that domain. So, as you can see I just changed registrars a few times and it hasn’t been dropped or else it’ll say one drops or two drops.
HIM: "Mainly small-medium sized local businesses looking for a way to increase their ranking. Most already have a branded domain in place, and have heard that using a keyword domain can help. Or they have seen a competitor ranking using that method. The problem I face is that they don't have a lot of money to spend, so I get lowballed on the asking price. There have been a few that make a ton of profit vs what I purchased it for, but that boils down to luck: what is for sale, when I find it, things like that."
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.
Where do I start? So I heard about bitcoin and I know it’s all the craze nowadays. Let’s start from there. I’ll hop on Google Trends and type in “bitcoin”. Google Trends basically tracks the popularity of search queries over time, it’s often a goldmine for discovering currently exploding or soon-to-explode topics/terms..etc. So here’s what it looks like:
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