bro, i got news for you. whoever you bought it from KNEW it was skimped...trust me. Most likely, she thought you wouldn't be putting it on a scale, so she pinched out a blunts worth (or a few bowls).
Idk if you were buying schwagg, because i've seen small time regs dealers eye ball their sacks, but no body who sells chronic eye balls their shit, at least down here...especially a half zip, which costs a decent amount.
if you get skimped, its your job to confront them. that doesn't mean show up at their house with guns blazing; be diplomatic (a phone call is usually best). its just a matter of letting them know that you're on point, and you expect the same from them. they may not be happy about you calling them on it, but if anything, they'll get over it and respect you more. if they don't start giving you better weighouts, stop buying from her.

my advice - buy from a friend that you know and trust. if you can't do that, make sure you're always on point with everything.

hope i could help.
pz