[swiley]

Oh wow I didn't think about that but yeah! the valuable ones tend to have holographic film and other weirdness that would make them slightly heavier.

[bombcar]

This could easily be defeated by simply having a holographic card in every pack - just most of the time it's a relatively worthless one.

[graywh]

TPCi started putting different filler non-cards in the packs and it's been hard to weigh them for years now.