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.
This is not surprising - these exchanges are totally unregulated and a perfect playground for scammers and cheaters. There have been warnings for more than a year that manipulation which is illegal in normal investment markets is rampantly out of control in the crypto markets.