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.
When I first started online, I'd register domains that I thought I could develop and sell at a later time. After learning my way around the cloud, I realized many of the domains I'd registered are pretty much useless, or so I thought, and I let them expire. Come to find out several of these domains have been picked up by parking sites and are being offered for sale for thousands of dollars! Now I'm not saying they're actually selling for the asking price, but I learned my lesson. I never allow a domain name to expire. I add content to it, backlinks, some AdSense and try to sell it for something.
Keyword relevancy is not the only thing that matters when it comes to SEO. However, domain names that were previously used by other businesses usually have a lot of backlinks and a decent ranking on PageRank. Even though such domain names are usually about to expire, they are still worth a lot of money if they have a good number of backlinks and a ranking of five or more.
Most of the website owners interested in an expired domain that has existing traffic, backlink and good SEO metrics. This kind of domain more likely gets buyer easily since it has a plus value for search engine optimization purpose. You can find high-quality expired domains that have SEO metrics by using BuycomDomain - The Expired Domain Search Tool for free, as seen in the picture below.
By default we show the following metrics - Age, Ahrefs Domain Rating, Moz Domain Authority, Moz Page Authority, Moz Trust, Majestic Seo Trust and Citation Flow, Alexa Rank, Moz Referring Domains, Majestic Seo Referring Domains, Open PageRank, SimilarWeb Rank, SEMrush Monthly Traffic and Domain Price. Apart from these there are around 40+ metrics that you can see by customizing columns