This is precisely why I didn't hold auditions. It's one thing if you're offering professional pay -- then, you don't have to worry about people showing up -- they will show up for SAG salaries. But if you're like me, and you're working with volunteers, or people who are willing to work for peanuts, trust is extremely important. On shorts I've produced in the past, people have commited to show up, and seemed genuinely interested, but then flaked. I got tired of that, and found that working by reference alone works much better for me, at this ultra-low-budget level. I had the good fortune of working with a dude, on a 48HFP a couple years ago -- not only was he talented, but he really took his craft seriously, and was very dependable. I figured -- whoever this guy trusts, I can trust. I've been working with his group of friends (a large pool, from a theater dept.), ever since, and it hasn't gone wrong. If you can cast people you can trust, you need no backups.