I host a lot of swaps, and I have that trouble quite a bit. My solution has been our swap of the month group, which is an ongoing swap with the same participants. For the portions I host, if you are a no-show or your entry is late, your name is off the list. This year, I am letting people host a month, so their portions are more lenient. I've tried in the past to be more lenient, but the more lenient you are, the worse some people are about the deadline. And it isn't fair to those who make their deadlines. IMO, the chronic late entries are worse than the noshows. And that is just as bad IMO.
The only problem I've seen on this site is that the no shows tend to sign up for one or 2 swaps, and then don't do it again. I think it either results from unexpected circumstances or not realizing how much time it takes. It seems about half and half on whether I get a response or not. In most cases, they didn't sign up for swaps again for a while. I went through some of my older swaps and tried to see if it was the same group and it tended to be different people.
Better to be an active environmentalist than and environmental activist.
FFMIRSWTNBOF (Full Fledged Member in Raunchy Standing-Within The NBOF)