A suspiciously high number of backlinks from some related niche websites that aren’t too great in quality. In my opinion, this could be an indicator that the domain name was using a Private Blog Network (PBN) service or their own PBN to boost their authority…this blackhat tactic can work, but it places your domain name at risk and the PBN owner could pull backlinks at any time.
It is much harder to sell names no one has heard of. Short names have the highest value — they are rare, easy to sell and bring substantial profit. Basic and common domain names, which can be relatable, or arouse interest in the market are the best. General names sell thick and fast and also bring considerably higher profit.  Names that are easy to spell will attract buyers, and provide good opportunity to make a decent profit. If you know you have a good domain in your hands, then you are likely to make good profit by selling it.
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.