Proofreading Help

How do self-publishers go about getting their short stories proofread? I know I could ask friends, but if it's something I don't necessarily want anyone to read until it's published, how can I trust a proofreader not to steal my work? It's a scary thing.

I'm pretty good at proofreading, but I can sometimes see words that aren't there just because I know what it's supposed to say.