Their Experiment + The Ending

So they're out there to tape their baby powder 'experiment' & sell the footage to a ghost show, right? But they didn't even tape themselves applying the baby powder! Who would pay money for that footage? It proves absolutely nothing! I get that the whole reason was to later have the footage of the guy's ghost behind them, but come on, at least TRY to give the attempt a little credibility. Not to mention, I would have taped it from outside the car, to watch the actual prints forming on the bumper. But we all know why no one does that...

Also, why are some people so confused about the ending? This was not open to interpretation, people. They made it really obvious what happened. It's debatable as believable, of course, but what was unclear about the ending???