There's a wealth of information to spill out on this subject but I'll try to condense it to both crush your dreams as a domain mogul and to complain about the whole domain market as a whole...
First off, the market has changed. I knew a guy who made his millions back in the hayday of the internet because he registered every domain name he could think of and did just what you describe. He sold them off one by one or in bulk because back then you could.
Nowadays, companies will build their businesses around a domain they can secure. Perfect example is damn near the worst domain name I have ever heard of yet and I am a web programmer - zoosk.com - just plain WTF?! Not a word. I can't imagine an acronym, I have no idea what would be the appeal of this fairly forgettable pile of trash for a business name EXCEPT that it's 5 letters long. The point being they found what was available that fit their parameters and just went with it. I don't know or care if they still exist, but if they don't I have an idea why. Chances are they wanted something else but didn't want to give some greedy chode the satisfaction of bilking them for a hundred grand so they opted to use a non-word and just make it work.
Nowadays TLD options exist as well, though the world may not be ready to break free of .com, .org, .net, .co.uk, etc. But the options are out there. So what is more appealing to you? someexample.com or some.example? well, suppose you thought to look for someexample.com and you try to turn it around for a quick profit and all that results in is your only buyer registering some.example instead? Well, your model then changes from registering domains that are available, to strategically registering the entire bulk of domains that could possibly be derived from the original concept. That could cost you a fortune. BUT WAIT THERES MORE - you get to pay that fortune annually until you can unload your mistake on the next dot com failure. You willing to bank on that deal? I'm not, and I know a guy who did this for a living. A very successful living.
The era of registration games is past. There may still be opportunities, but not quite so simply as you outline. Yeah, you might get lucky. Every now and then someone sends me an email asking to buy one of my domains but they never offer enough to even warrant a response to the email. Unless you have a good amount of savings to live off of, I wouldn't recommend casually entering this market. Do it for fun if anything and see how it pans out.
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If you want to register a domain name, do not search it until the very second you are going to register it. You can safely search in console or terminal but never ever in a million years use a web form like godaddy's domain lookup to see if its available. Those greedy sacks of feces will register the domain if you don't buy it immediately and offer it back to you for hundreds or more. If they decree it a "premium" domain they do exactly this and it is completely and utterly legal. It won't work if you mess with them by smacking your hand on the keyboard and looking up "vlhadsvcblsa.com" - they're not stupid. but if you looked up something with real words... jennysdiner.com for example. you run the risk of them grabbing it while you ponder your future. No kidding, 20 years ago I typed in the name of the 6th level of a video game called space harrier and I accidentally mistyped it. 24 hours later it was registered and parked, offered as a premium. It wasn't even a real word. Just mish-mashed gibberish. Never again did I use a search utility.
Another option - I used to work for a company that registered trendy domains, made quick and simple ecommerce sites out of them, then sold the sites while they were hot. There's a certain degree of science behind this. You have to know and predict trends, build fast, SEO the hell out of it, and find buyers so they can get in at the peak, make their money, and get back in line for your next trend. But this helps on the legal front of things as well. If you actually run a business or otherwise populate the domain with viable content you gain legal stance if someone decides to try to sue you for it. To some degree. If you had pepsi.com you're probably going to lose no matter what. If you had bofa.com they would have little grounds to snag a pet name if you are actually using for something. maybe thats a bad example cause you'd never get either of those, but say there's a new spiderman movie coming out. If you got spideyspinners.com and threw up a quick fidget spinner site revolving around spiderman you might not get dinged for it and may be able to move the domain and business before the trend died.
In short, it might help you to actually develop the domains you intend to flip. Valuations have many factors beyond just number of letters or buzz words.