Let's take for example:
This one says 1080p in the title, but it's not an HD or FullHD version, if you look through the description, it says 1280x480p... which means it's LOW RESOLUTION. You might think that's ok, but in reality, let's say someone hits you and runs, you might not even be able to make out the license plate because of the low resolution. Don't fall for these pieces of junk.
Make sure the resolution in the specs are at least 1920x1080, that is the only real 1080p FullHD.