According to the rules given by the Ogame Go's/Moderators all trades must stick to these trade ratios,
3:2:1
or
2:1:1
Obviously a higher ranked player can send resources to lower ranked players without the lower rank player having to return anything as long as this was agreed by both the higher ranked player and the lower ranked player. If a lower ranked player sends resources to high ranked player without the higher ranked play returning an equal/equivalent amount of resources then the moderators may think there is pushing going on in which case one or both players could be banned!