If you send a bubble 000 envelope, my PO charges $2.07 without checking thickness or size.
At the University PO at work, they check size and thickness and charges $1.07 (a couple ounces).
If they put stamps, it comes back asking for another $1.00.
If they use their meter sticker, it doesn't come back.

Insist on a metered postage sticker!

Inconsistency drives me crazy...no wonder the public has a bad opinion of the PO.