That's why I no longer cast one actor for any role and I am refining my system for backup actors. I cast leads for more than one role.
With low/no budget casting, most of the actors coming your way will be untrained. lacking with the ability to act, spreading themselves too thin, and are down right flakes. This past Sunday, I had 7 actresses coming in for one role. Four flaked from the night before right up to less than an hour before.
For the 3 that showed, one is fresh out of school and rusty with her stunts. She needed coaching with her reading, but got better. The second just isn't cut out for acting and has no range of emotions. The third was BRILLIANT and aced and double audition. She audtioned for 2 roles and was brilliant with both and is very interested in working in my production. So, she's in. This coming Sunday 2 others are coming in to audition for her bigger role. I told her what was going on. She asked me to let her know what she would have to do to top them to retain her front runner status.
Always cast more than one actor for any role. You never know.