When you start out, it is always difficult to convince people, who don't know you, to give their spare time to you. I started with asking friends and relatives to build a portfolio.
@OP:
Do you already have a portfolio?
Most actors (m/f) look at casting calls like this:
- Does the idea sound interesting/fun/cool?
- What quality does the previous work look like? (Will it make me look good? Will it add something to my reel/experience?)
- Can I affort to spend this time on a project?
- Does it seem like a legit (non-scam, no pie in the sky) project? (Can the filmmaker pull it off?)
And then there is the whole art of writing casting calls that can really make a big difference. It has to read like a serious project, yet full of enthousiasm without rediculous claims and it needs to contain what the role asks from the actor/actress (no surprises on set!) and when you intend to shoot (makes it easy to plan). Also be clear about whether or not you will pay travel expenses or not. (I usually do "as long as you don't hire a helicopter

" ) and make sure you provide for food and drinks on set (and say that in your casting call: it shows you care about your cast and crew).
I know it can be done.
I only pay actors (m/f) when it is a paid (commercial/corporate) project. However, on my own projects I do reimburse travel expenses and of course I provide food and drinks on set.