"You sell something to another empire cheaply. The other empire puts the same stuff at the market at a higher price and you buy it back."
In that case, throwing a 3rd empire into the mix would make the cheating undetectable. Example: Empire A sells 1 million minerals at 500, Empire B snags it and reposts it at 800. Empire C, and maybe D and E who happen to be in the fed then buy it up. They then repost again at the max and Empire A buys it. This process happens over a period of 4 days.
In such a scenario, an admin looking over the transactions wouldn`t immediately see anything fishy, even if someone reported it. Only someone looking closely at this complex pattern of dealings over a period of several weeks, and looked at fed affiliations may notice something.f But if the transfer isn`t blatant, it would, again, probably be glossed over.
If the money launderers are able to obscure their intent and no one reports it going on, no one would ever be the wiser!