Very good article and overview explanation. However I would not recommend buying names with bitcoin, ripple, etc in them. Not only will it be oversaturated those names are brands and can / will be trademarked and you can still be hit with a UDRP. Only register generic names like buycrypto.com, buyingcryptocurrency.com, theblockchain.com, etc. There are tons of opportunities and no need to infringe on a brand name.
To sell a domain name, one should learn to price it. Many sellers fail to sell names in the marketplace, simply because they overpriced the domain, and thereby lost the chance to sell it. A lack of knowledge leads to erratic pricing. Experienced buyers will not try to bargain, unless you have a very rare name. A seller should therefore, understand how good the domain name is. What price will he get from a buyer? What suffix does it carry? For instance, .com names are likely to sell fast and will bring greater profits than, say .info names. Similarly, .net, .org and .in domain names are the best to make decent profit.
The easiest and least time consuming option is to 301 redirect the old domain to your existing site. This tactic obviously works best if both sites are in the same sector and are targeting the same keywords; otherwise, if you have a pet supply site and you buy an old Texas Hold 'Em poker site, a redirect probably might raise some eyebrows among the search engines. If, however, your site is brandnamepets.com and you buy onlinepetsupply.com and 301 redirect the domain over, you're inheriting a lot of topical and appropriate links.
Your course of action really depends on how much work and effort you can put into the expired domain. If you're barely able to maintain and optimize your current site, you probably want to just 301 redirect the old site (note: see my amended comment above about the link value not likely to be passed). If, however, you're more creative and have some time on your hands, you can try your hand at crafting a microsite. If you really know your stuff and are experienced at making money off various websites, you'd probably do well with the third option.
If domains are real estate, then the same rules of real estate should apply. In real estate, taxes are based on the value of the property. So, a person asking $10,000 for a domain shouldn't be paying the standard $15-30 renewal fee as a person asking $200. The renewal fee should be based on the domain's value. Domainers want to claim it's like real estate without applying the most fundamental rules of real estate.
The domain name industry is quite similar to the real estate industry in a lot of aspects. There are end users, brokers, consultants and domain flippers or “domainers”. Domain flipping works similarly to buying a house, renovating it (or even sometimes just sitting on it) and then selling it again at a higher price point. The gist of it is: you’re purchasing a domain name and betting it’s worth (or will be worth) more than you paid for it. If you’re right, you get a nice paycheck and move on. Those who make a living out of this just rinse, repeat, and scale.