Hi thanks a lot for this. I appreciate your honesty. A lot of people need to hear this. I needed this to. When buying and flipping domains always ask yourself who would actually buy this domain, what they can do with this domain and how would you monetize this domain if you bought it. Always think of your customer and treat it as a business. I think you’ll avoid a great deal of dissapointment down the line. Thank you

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.
Surely if you purchase a domain (domain1.com) and redirect it to your existing domain (domain2.com) you expect to loose all ranking for domain1.com. If 301's are used then the objective is simply to pass on authority, not dominate the search results with 2 domains. If you want to keep domain2.com in the index then you would take Rebecca's option 2 or 3.
Many individuals have the habit of collecting attractive domain names but never using them. If so, why not get rid of unused domain names and in the process, make some cash? It is important to understand the whole process of selling domain names. On the outside, the process may look very easy, but unless a trader is well aware of how the whole process works, it is not easy to find a buyer.
Hi, I’m Mark! I’ve been an online entrepreneur, writer, website flipper and more for over 8 years now. Having faced the highs and lows of the online marketplace first-hand, I’ve learned quite a few things along the way. I’d love to share all those learnings with you here on this blog! Buying/selling websites can be great fun, provided you’re aware of the right tactics and know how to implement them correctly. My posts will help you do just that!
I OWNED DOMPERIGNON.ORG, incredible, but true.  Lost it, back in the days when internet in India was not a readily accessible utility. And I was a casual domainer.  You had to go to a cybercafe. Did that late in the day, towards the expiry of the domain. No chance of renewal. The domain is now with the owners of Dom Perignon and is redirected to domperignon.com! 
Just because someone spent five or six figure amount on a domain name doesn’t automatically imply that he/she’ll spend the same or at least a few thousand dollars on a similar name too. Basing your domain flipping strategy entirely on what others have just bought may not be as useful as you may think. Every domain name has a story behind it and its purchase/sale is usually as unique as that story.
Dictionary Word/Pronounceable/Memorable/Brandable: A dictionary word domain name is very valuable. Of course, the more popular and widely used the word is, the better. For example, “marketing.com”, “cars.com” and “hotels.com” are 7-8 figure domain names. Even if a domain name isn’t a dictionary word, being pronounceable and/or memorable and/or brandable are all big pluses that add to its value.