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.
Of course, they will do that. Crypto world has become very much filled with these suspicious activities which affects the trust of all investors.
An experienced investors might be able to spot such manipulations done by big entities but new investors will fall for this and suffer huge loss. Best option for them is to invest in coins like bitcoin where least manipulation is possible.