(Sample Projects) -- Hey, if you wanna pay me to do a sample project and then also pay me to do the actual project, fine. I can see how that would work if the sample project is a small subset of the actual project. If you expect me to do work for free in hopes that I can do work for pay.... yeah, no.
(Goal Alignment) -- In any business, the service provider should have an investment in the client's success. Primary goals might not be the same, but if the freelancer isn't doing it to help you -- you have a bigger problem.
(Hourly vs. Fixed Price) -- I imagine any issues with fixed-price contracts can be avoided by going over requirements thoroughly at the outset and having a good agreement set up in writing. I've been bitten by this before, but I know it was my own fault for not setting things up right at the start.
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All in all, I think a better though process for this blog post would be "How to Hire (better) Freelancers" or something.