but its a crime against humanity if they charge more than the exact postage.

As PJ said, but also, it is crime against all the honest sellers who only charge what it costs to post, and pay fees on the rest, while the cheats who load the postage cost do end up with less fees.  Therefore overcharging on postage is dishonest, and if seller is dishonest = ripping off eBay, why should the buyer trust them they will not also use any opportunity to rip them off?

And again, I am not talking about few cents for bubble wrap etc.