Actually, the place across the road is an LPO, so perhaps that's the reason they're not policing it. You can also drop off your dry-cleaning there to get done...

Most of my items tend to be well under 500g, so if on occasion a 520g item ships in a 500g satchel...I figure AP is still ahead overall 😄

I too have been shafted by Ebay's non-sensical postage calculator, and to prevent this, I have sometimes put a ridiculous weight in the listing, if the buyer is too impatient to wait for an invoice, they would have paid too much. Once I have actually worked out the proper postage, I refund the excess.

Don't you then pay excess fees, as postage is now included in the total of your Final Value Fees? Refunding the difference usually isn't taken into account, you're charged based on what you invoice and is initially paid.