Good deals do exist on eBay, but they are not the norm. As with shopping anywhere, if you don't know what you're buying and haven't done your homework, then you end up paying too much. The differences with eBay are that there are many more buyers and sellers in one place (i.e., more opportunities for stupidity, nonsense, and shadiness) and people get swept away by the desire to win (and end up losing).
It is unfortunate that the stupid ones ruin good deals for the smart shoppers, but c'est la vie. More patience is required.