[Alneyan]

You can't figure out *what* exactly is offered for trade, though you know the names of the items to be traded. By the way, any entry under Systems is pointless, so be wary if someone offers those to you: it should remove claims over the system, but I'm not even sure if *that* works, and it won't affect the colonies, ships... in the system.

Other than that, you just have to trust the other player. Ship trading is particularly risky, given all the opportunities you have for deceit here, and I think you can also promise to give a lot more resources than you actually have (though it will create some trouble for your own economy).

For ships though, you could put a Long Range Scanner and require to scan the ship before trading. It will only work on ships without a Scattering Armour (or the much rarer Scanner Jammer), of course. There is no such trick for planets or resource trades.