Getting free consultancy from freelancers

Recently I spent quite a bit of time with a potential client, after I was invited to an interview on oDesk, discussing his project. I discussed a lot of technicalities of the project, even before he prepared the spec, giving my input and expertise in preparing the technical specifications of the project.

This was a Windows Mobile project and involved printing from the device using a Bluetooth printer. The client, though he was a techie, did not have a clue on how to accomplish the printing task, as I had already done this before on another project.

That was one of such incidents, there were quite a few other issues. In terms of how the applications was going to communicate with the server application, how to store the settings, how to store the application data in the device, how to handle situations when the connectivity is lost, etc.

After all of that, I was informed by the client that they had decided to go for another provider who quoted a lesser rate. I had spent hours of my time and shared my expertise free of charge. I basically feel robbed.

How do you handle situations like this in free lancing bidding phase? You need to share your expertise in order to convince the client that you are the best man for the job. And then the client gathers this expertise and goes elsewhere.

I assume this scenario also applies more to the web designing jobs as well. The clients may ask us to submit a proposal, which would include a concept for their web site. And then they run with our concept. What are the safe guards, us freelancers have to protect ourselves from such scenarios? Any ideas?