Is it the push account rule, you mean?
"... Trades in any form (goods, Forge Points, etc.) that involve multiple worlds are forbidden… "
Fps for goods trades are made between guild members and friends in the same world; not across multiple worlds. Or sometimes a generous friend or guild mate just gives away the higher era goods for free (= for lower era goods).
A friend of mine (in the same world!) recently gave me SAAB goods for EMA goods, so I could build the Space Carrier from SAAB. That's not against any rules - and it shouldn't be.