RE: Engine / Prop Vibration
Sand or scrape the top of the heavy blade. Don't scrape or sand the flat side as you may disrupt the pitch.
A couple of suggestions from one who has balanced a TON of props over the years........
...When you have a prop that's very obviously way out of balance, put it aside. Next time you're in the LHS, ask if you can swap an unused prop for "a different one".
...When it's obvious there is a heavy blade, look at it. Good possibility that you'll see that it's thicker toward the TE than the light blade(s). If it's also thicker at the LE then look carefully at the width of the light blade. Sometimes it's obvious how the heavy blade wound up so much heavier.
...You can fuelproof with CA or paint. The faster a paint dries, the less it's going to add weight. I've got some clear lacquer that I keep thinned out that works great for me. (You don't have to fuelproof composite props (Yes, I knew a newbie once who was painting the sanded blade of his plastic props) but you can paint the light blades if you wish.)