Excellent info. from Night Wing. Another good place to check is
www.bowmaker.net --great tuning advice there.
Just going on what you said, I suspect the guy at the store sold you some arrows he needed to get rid of--arrows already fletched with feathers, plus he didn't bother even watching you shoot to see if it could be a form problem rather than an arrow problem.
You might try heavier points, but I'd see what the calculator says first.
Chad