I'm glad I'm not the only one! When I go through and check on people wanting in the swap and see that they have instances of being late, I PM them and ask why they have them and if it sounds fishy, I've PM'd the organiser and asked about them. Is that horrible?
I also followed Kristen81's example and if you haven't sent out within (I think) 5 days after sendout, you receive a negative until you send. I will change it to a positive, but lateness is noted, as is communication. Some people get mad, but if I'm late, and I have been, I'd be okay with it.
I think it might just be difficult to institute a probationary period and keep track of it. You might need one mod just to do that!