Buying and selling domain names is an exciting adventure that for some seems to conjure up images of finding hidden pirate treasure or guessing the winning combination on the next Powerball. Stories abound of domains that were purchased for $8 dollars 15 years ago being sold today for millions. Of course, that leads the more adventurous of us to wonder, “How can I do that?”
1) pending delete auctions.  These are domains that were not renewed and are going through a pretty complicated drop process.  You can backorder these names at the auction venues and then each attempts to "catch" the dropping domain.  If one is successful you win the domain at $59 if you're the only one to backorder the name.  If more than one person backordered the domain a 3 day private auction is held.  Once the domain goes through the drop process, the back links have pretty much zero SEO benifit to the new domain owner.

Most of the website owners interested in an expired domain that has existing traffic, backlink and good SEO metrics. This kind of domain more likely gets buyer easily since it has a plus value for search engine optimization purpose. You can find high-quality expired domains that have SEO metrics by using BuycomDomain - The Expired Domain Search Tool for free, as seen in the picture below.
Some people in the advertising and marketing industry have expressed fear that considering the way social networking portals are taking over our lives, businesses will soon operate from these websites and stop building their own websites altogether. Although such fear is justified to a certain extent, if looked at thoughtfully, the benefits offered by an independently hosted and controlled website far outweigh the promise held by social profiles.
The third option is the one that's the most time consuming but also has its benefits. It's like having a successful restaurant and buying another restaurant and operating them simultaneously. They're not the exact same restaurant, but both are popular in their own right and make you money. The same goes for Option #3. You could update the content on the old domain and sell the same products that you're selling on your current site. If you can get both sites to rank alongside each other in the SERPs, you're increasing your conversion chances and sales potential.

Just because something is legal does not make it ethical. While things that are legal can and often are ethical, there are practices like domain name flipping that are not ethical. Buying a domain name without intending to use it to make profit creates an unnecessary industry which costs people money and reduces general productivity and economic growth. This is the same with all practices that cost people money but do not contribute any value, most notably corruption. If we eliminated such practices our economic growth increases and general wealth is increased because our money is paying people for things that add to our lives and our communities. This does not. Evessariky reglect badly in people who choose to engage in such practices, but is a result of regulatory failure.

Choose Niches that make money: People will buy a website domain if they think they can use it to make money. So buying popular phrases/words that could be associated with selling something like computers(.com) or hotels(.com) could be used by a company to sell computers or hotel reservations. However, something like Warof1812(.com) may not have the same business potential.
Building a solid domain portfolio is not a piece of cake; it may take you several months or years to achieve this goal but it will definitely be worth it in the end. When you are in the fishing phase, look at the potential of the domain name. Another common strategy used by seasoned domain flippers is to get hold of some high profile domain names and sit on them until they soar in terms of value.
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 a lot of guesswork that goes into domain name investing. It's not enough to purchase domain names that are currently popular. Just like a stock, coming too late to the game won't be profitable. You have to think of the future, instead. What domain names might be profitable in the future? Is there a new product or service that may become a huge hit? Where is the future headed?
That said, my recommended budget for beginners would be $500+. Using this budget you could buy a bunch of high-potential $10 domain names, expired/dropped domain names or a mix of both. It’s very important to invest only what you can afford to lose and treat this as a side hustle till you get the momentum going. As you gain experience, industry expertise and some sales under your belt, you can then consider slowly growing your business into a full-time gig.