This is something most indie authors would have tried at some point or the other. Believe me, been there, done that. It’s a momentary high. The object is simple. You need to get your books high enough on lists to ensure that they are noticed. How does that work? The more number of books that are sold, the higher your book shows up on an amazon list. So, if you can get a number of books sold in a short period of time, you could even climb to a number 1 spot in some lists. For those who haven’t tried this and are wondering if they should, let me disillusion you. It stays up for maybe a day, even less. Yes, you do get a few extra sales, a maximum of up to five, but of course that would depend on your genre, reviews, audience etc, but on the whole you maybe break even or lose money because you are buying (let’s say that ten people are swapping) ten books and you will pay the tax etc on those buys. You will only be getting royalty for your books which are bought by the others in the buy/swap.
Other than being a good Samaritan, and making money for Amazon and getting a few screenshots of your book on the #100 in some vague list, it really doesn’t mean much. But hey, that’s just my opinion.