I used to do tons of swaps. Sometimes I would get back cards, ATCs, etc that were simply magnificent! Other times, they were "barely there". Most often people sign up early, forget to make a note of it, fail to mark their calendars, and reply to my reminder posts that they just forgot and ask if it's ok to be 1-2 weeks late.
I got tired of hosting swaps, trying to be nice and wait on folks. More than once I declined a request to join because I knew that person had a history in my prior swaps of not meeting their commitment.
The best swaps came when I personally invited people who always sent in great work - on time. I also hosted "newbie" swaps intentionally designed for folks who were brand new to the craft and to swaps in general. Funny, not a single one of those folks was ever late with a delivery, though I had to do a lot of 1:1 personal counseling to convince them to send me what they had created instead of dropping out for fear their work wasn't good enough to share.
Swaps can be fun - choose wisely and don't set your personal expectations so high that you will always be dismayed.