There's a reason it is the one of the most common things that people advise to newbies. There are two ways to learn what makes a domain name valuable and which ones sell. One is to gain first-hand experience by buying a ton of domains, pricing them, and actually (hopefully) making sales. The other is to read what thousands of other people are collectively selling. One of those approaches takes years, lots of money, and lots of risk. The other just takes a little effort. Guess which one is which
What you have illustrated, however, is that domain+price is not the entire picture. And I absolutely agree with that. Lots of the sales that leave people scratching their heads were actually sold because they were a developed website before and have lots of backlinks, and presumably traffic as well. So Archive.org and Moz are good places to check when you're feeling confused about a price. But there are so many other factors to consider, like how many companies use the name, search volume and CPC numbers, sales velocity of the keywords, and on and on.
There are too many to discuss in this post, so I would direct you to this video of a DNAcademy tool that aggregates the important things to look at:
It's a useful watch even if you don't have access to the tool itself, because it shows you what areas to be checking when you want to *really* understand why a domain sold for what it did.
You have to dig deeper to get a better understanding, plain and simple, because there are a lot of nuances in this business. For example, let's say you see three-character .com sell like 7b2.com. Then you assume all are worth a similar amount. But when you really start studying CCC.com domains you'll understand a lot of the value drivers like:
- Pattern matters tremendously (LLN > NLL > LNL > NNL > etc).
- Some letters are better than others (Chinese Premium vs Western vs Neither vs Both).
- Some numbers are better than others (0 and 4 are bad, but not always - think P90).
- Repeating or sequential characters have huge value (aa, ab, 88, 89).
- Having actual meaning trumps all, like N95.
Just blindly reading sales reports and going out trying to buy similar names without doing any homework is definitely a mistake. I don't think anyone was suggesting that though.
Otherwise you see GrassX.com and think "Hmm, Grass + Letter = Value". A slightly deeper understanding would tell you single letters as a suffix are sometimes valuable. A full understanding would tell you that X is a very popular suffix to add to a word, but most other letters have no value as a suffix. And with that full understanding you could search for Good Word + X .coms that are available to register, or keep an eye out for those types of names on the drop auctions.