There are several types of domain names to avoid. One is intentional misspellings, as these make it less likely someone will search for them. You also want to avoid names with extra symbols like hyphens, or with added prefixes and suffixes like "e" or "my." Outside of a few notable exceptions with very strong brands (like eBay), those additions can only hurt the value.
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.
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.
Once you decide to sell a domain name, it is important to find the best market to sell it. The best way to sell a domain name is to approach buyers secretly. If you know someone who deals with domain names, it is recommended to contact him without going through the middleman. Chances are that the seller will make more profit, as he will not have to pay the middleman.
They see a domain’s price tag and they can instantly tell whether it’s under or overvalued. This is probably the most important skill one should have in this industry. Neil Patel has an interesting related quote: “The most important thing to remember when buying sites is that you always make money on the buy, never the sell.” In order to successfully do this, you must be able to spot undervalued domains. This is what will ultimately translate for you into a handsome profit margin when you get the opportunity to resell the domain for its “real value”.