Hey 
@M0nolith good post. 
Just a quick headsup for discussion type threads I would post them in future in this area of the forum - 
General Discussion. No big deal but basically more people will see it as this support area is for poker rooms and our sales/support guys. 
Anyways onto your question. I have 10 years of buying, sell, swapping and staking so I hope this answers a few of the questions. 
Swapping: Simply put people who rate themselves equally before a tournament starts will swap some equity. So normally you will swap 10% with one another. What this means is then if you cash and your friend doesn't you give him 10% of that amount. It basically gives people more to sweat for and limits the variance slightly. If you have heard something like "I am all swapped out" in say a live EPT TV show they may have swapped 5 or 10% with 5 or so different people. It just makes it more fun, gives you more shots of winning and when multiple people go deep it could be a huge payday. 
Selling: Simple people will sell for a few reasons 
- They are not bankrolled for an event/Taking a shot. 
- Want to limit variance. 
So if an event is £1000 and they are selling at 'cost' then simply put 10% -= £100. Then if this persons does not cash the investor loses that £100 and it is forgotten. If he goes onto cash he then owes 10% of whatever that amount is to his investor. 
Now you may have heard of mark up. So something you may see a lot of is "Selling at 1.2". What this means effectively is that they are selling 10% of their action but it costs you 12%. The reason many people do this is they figure they have a 20%+ advantage over a field, wanting to sell lots so it costs them little or it is just what they have read/heard of before. So that 10% at cost of a £1k is £100 but at a 1.2 markup is £120. If said seller then cashed for £1000 the investor gets £100 back. 
Buying: Covered most of this above but the reasons to buy are normally pretty straight forward
- Rate the players chances. 
- Treat it as an investment. 
- Gamble. 
- Fun. 
So you can basically sit in your arm chair, have a piece of someone who you think is good, has a chance and can win a ton of money. 
We have a marketplace 
Here  where people buy, sell and swap for both online and live events. We invest on average $2000 per month. You should take a look and give it a try.