I think I might be coming in at this from a different angle than you’re asking, but what the heck.
I’ve picked up a few jobs here and there (as a service provider, not a buyer) on various “typical” freelancing boards such as oDesk, eLance, Freelancer, etc. A few things I’ve found is a ton of replies to your job postings are going to be copy and paste cookie cutter responses which do not necessarily address the job you’ve posted - rather they reek of self-important individuals or teams telling you more about themselves and how wonderful they are instead of addressing anything whatsoever about the job you’re actually posting. Common sense would tell me to stay away from these, but it doesn’t appear common sense necessarily prevails on these types of boards, so I thought I would throw that out there.
In terms of payment, personally I would never even begin to consider a job post if the buyer stated out front that there would be no payment, even milestone payments, until the job was complete, bug free and delivered. My standard procedure was typically to collect half before even starting the project, and then to either collect the 2nd half at completion of the project or collect partial payments as milestones. This would show me that the buyer was serious.
You may get lucky and find someone who fits right away, but I think your mileage may vary finding reliable, trustworthy, talented developers on those types of boards. As far as any worthwhile alternatives, I’m sorry to say but I don’t have anything to offer.