Sorry price DROPS instead of props, typing error!
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It is possible that exchages buy coins on some volume and then buy back but on lower price but at much bigger volume and make a lot of money on this?
I have no idea if they are doing this but if they do, they won't let others know this type of activity that they are doing. Also it's their choice to buy the coins that they think will have large volume in the future just like us traders.
This is why the exchanges are becoming richer quickly that has a lot of traders on their platform.