I should add that I also think that the system of approving trades also ensures that the host doesn't end up with a whole bunch of 'donated' seeds that they don't know what to do with. If everyone agrees on trades, including trades that involve a 'something for nothing'...then everything has a place to go and no one is left trying to figure out what to do with a million tomato or marigold seeds that they don't know what to do with.
