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.
Here's a test I have in process. I bought an old $5 closeout domain from Godaddy TDname expired auction. I put a quick minisite up and linked to it with a crazy anchor text phrase. The domain is ranking for that crazy term now. It's gone through one pagerank update and I'm waiting for a second to come. Then I'll redirect the domain to another minisite. I suspect the second site won't rank for the anhor text, but we'll see.
I have one domain name which I never used it and it has .com and I later discovered there is another company with similar name but with .net and they are doing good as once they approached me to sell them my .com which I never did as I had plan to start something which didn’t materialize . its been 11 years now I have maintained the name now I have two options.
Buying a website is a risky job especially if the investment is big. My first experience was a big fail. So after some time spent on Flippa I found out about a site called Safe Site Buying which I heard that was created by super sellers from flippa and got a coupon code "flippa50" which was supposed to give me a huge 50% discount. This deal looked pretty good to me so I tried it. They provided me with a full report, 20 pages long and with their own subjective opinion. They were very helpful. When you want to spend more than $2-3000 on a website this service is a must if you ask me.
There’s an important distinction to make here between domain flipping and website flipping. The latter mainly refers to buying and selling full websites. By full websites, I mean websites that actually have content and more often than not have traffic and revenue. When buying and selling websites, the domain name matters less as the main value there is the content, traffic, revenue, history/reputation, sustainability and growth opportunities. The same can’t be said for domain names where you’re just selling “the name” and hence it’s all that really matters.