In theory, anyone can do anything but they do have a reputation to protect. Being the largest bitcoin exchange, why would they risk their reputation?
Money... that's the reason...
Thing that they were not audited ( were not they? ) gives a chance that this can be happening... Sitting on such big pile of cash can shift your business practice.... They can be doing it with small % of the funds at their disposal just to gain extra $... but I don't think they can do it with amounts enough to move the market....
Anyway, it's my IMHO only... and they can be clean as a child's tear ( or maybe not
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