Found an interesting article in which one guy did some datamining on some popular exchanges and their volumes:
https://medium.com/@sylvainartplayribes/chasing-fake-volume-a-crypto-plague-ea1a3c1e0b5eApparently a few of these giants are falsifying their volumes. Maybe because a higher market cap would make people think it's a more trustworthy exchange? I don't know if it's really worth going through all of that effort.
Would this have a major effect on the prices? I know we used to see huge differences in prices in the past, but now you won't see much more than a few percent here and there between exchanges.
Yes that's the reason why exchanges fake their trade volume as if the trade volume will be more then more and more people will join the exchange because it will provide liquidity when the people will sell their coins as the market crashes if some large order is executed and there isn't enough liquidity.