How do you even do that? I don't think you can trade between servers?
You can't. It would have to be a two-step thing - say, we agree that you giving me 20m on Et is fair for 10m on LC; you give me the 20m on Et, then I give you the 10m on LC (or vice versa). That's why there's a possibility of one player deciding to scam by cancelling the trade in which they're giving money, as soon as the first trade, where they're receiving, is accepted.