I agree with what others have written. I'm offering seeds because I want to share them with others and I have more than I can ever plant. If I send 50 packs but only get 15 back that is fine with me! I'd rather get 15 packs of seed I really want than 50 packs of seed I don't need/want.
This is also where wish lists come into play. If they want specific seeds they don't see listed then they should put them on their wish list. If people see that, they may add to their swap list just to satisfy someone's wish. It doesn't always work but it increases your chances, especially in a large swap, of getting what you really want.
