1) They aren't serious, and are posting the project to get a sense of how much it may cost them to develop an idea.
or 2) They don't care or are ignorant of quality issues when choosing a $10/hr bid.
As developers, we scoff at badly written code - it offends us. But as a business person, especially the cheap ones, as long as it works and accomplishes the goal, you're happy.
You should ask yourself if that's who you want to work for. You won't capture every dollar posted using the method above, but it will filter out the non-serious and non-quality minded project owners.