Which trades are not allowed in game? What are forbidden trades via third party? Explain the threshold between two player.
When 2 players share ip and computer, there is not allowed any trade between them, no matter if is balanced or not. When 2 players share ip but not pc, there is allowed balanced trades, trades done with an average market price. When 2 players don't share ip or pc, any trade is allowed but with limits of "free" items or money that one can give to another, the limits always is according to the lvl of the one that receive, and they are between 2 players, let's say, you can give for free up to 100g to one player with limit is 100g, but then if you want to give to another different other 100g, is allowed, cause trades are separately.
When 2 players are married, it is allowed free trade always that they don't share ip or pc like we explained before, that rules go first in that cases.
Via 3rd party. Is forbidden to use another character to overcome not allowed trades. Example when you share ip and pc, you create a multi account just to give things to your main char, but as is not allowed in trade rules, you ask a friend to make trade with you, you give him things from your second char, and he gives back to your first char. In that case is forbidden and can be jailed the 3 characters, also the 3rd party.
Another case, when you want to re-roll. You can't give all your things to one person, re-roll, and then ask him to give you back to your new character. There is a premium service to do this specifically according to rules.
Cheers