best way to legally try to predict a holo pack:
If you are allowed to handle an individual pack before purchase, you place it on a flat surface (countertop). Make sure the ends of the pack aren't bent down, thereby pushing the pack up.
Then, gently push down on the middle of the pack with 2-3 fingers. Lift up and repeat 2-3 times. If you feel the pack "give" when you push, chances are you found a holo.
Holos tend to warp more than nonholos, thereby creating a "bubble effect" this way.
Works for most card games, esp. LOTR where foils are very scarce.
DON'T bring a digital scale to the store to weigh the pack. They will not like that.