I wouldn't use the word "sell" because only authorized merchants can legally sell Disney tickets. However, unused tickets can be "given" to anyone you wish.
Your problem is that they are linked to your MDE and cannot be unlinked. You can transfer those tickets to any friend or family member that you have in MDE but if the recipient is outside of your MDE circle, they will not be able to add the tickets to their own MDE.
And here's an even bigger problem...if you have multiple tickets in your MDE that you want to keep for yourself and you "give" those unwanted tickets to someone else without them being a part of your friends/family, then Disney might take days off of one of your older tickets instead of the recipient's ticket. Just as an example:
- You have 4 passes in MDE - 2 5-day passes and 2 4-day passes. The 5-day passes are older and are assigned to Guests "A" and "B". The 4-day passes were purchased more recently and were also assigned to "A" and "B".
- You decide to "give" the 4-day passes to a friend of a friend of a friend. I'll call them "X" and "Y".
- X and Y go to Disney with their 4-day passes which are still linked to A and B. They use them at the gate for entrance, but because they are linked to your MDE account, the computer looks for the oldest tickets linked to that MDE account and takes 1 day off of the 5-day tickets instead.
- X and Y don't know that this is a problem and spend a happy 4-day visit at Disney. Months later, JohnDaleswife goes to Disney for a 5-day visit. On Day #5, she can't get into the parks? Why? Because X and Y used the 5-day tickets and the 5th day expired. JohnDalesWife and friend have been using the 4-day tickets.
So, without getting even more long-winded with my explanation, you cannot just sell those tickets to a stranger once you've added them to MDE.