I don't see where it is unfair. What if there is one pack of seeds available (in just one swap) that someone wants. Another person is there right when the swap starts and selects that pack of seeds. The first person that wanted it was at work and was unable to be there at the beginning to try and pick it. Is that fair? Everyone is not going to be able to get every pack of seeds they want. Now if I only had one pack of seeds available I would probably choose just one swap, but I don't think it is unfair to list it in more than one. Also by creating just one listing and putting it in more than one swap you are not having to guess which swap to put them in or how many to put in each swap. If you put them all in one swap you might not get any takers where you might have in the other swap. Or you put 5 in one swap and 5 in another and one swap sells out where the other no one takes any. Putting them all up in both swaps puts them in front of all participates and gives you a greater chance of giving them out.
