Those trading domains for commercial purposes are generally on the prowl for lucrative domain endings. There are essentially two different ways traders go about making money off of domain names. One method entails purchasing already established names for a low price and selling them for a profit later once their value has increased. Another strategy involves buying and registering a domain that is thought to possess a high sales potential. Many domain traders use backorder services. These services automatically register a domain when one becomes available or is deleted (what are known as expired domains).
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.

You can’t tell us (with a straight face) that aged dictionary word .net and .org domains won’t sell easily. The .net extension is technically OLDER than .com, and holds an equally intrinsic value to that of its .com counterpart. These LLLL .com’s that are just letters slapped together may be cute to look at and easy to sell, but in the eyes of Google, ANY aged domain that makes sense (i.e. a dictionary word) is going to be much easier to rank for than some acronym or hodgepodge .com…and at the end of the day, that holds more value than whatever society sees in these nonsensical “” names.
In order to maintain ownership of a domain, you must renew it yearly. If you don’t, it “expires”. An expired domain goes through several stages before being released again for general registration. The process differs slightly from one registrar to another but it’s more or less the same. GoDaddy explains what happens to domains that expire with them here.
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.