So its ok for a seller to buy an item for $1 and sell it for $100 but its a crime against humanity if they charge more than the exact postage.

Not a crime against humanity but certainly a breach of ebay policy, the only ones missing out are ebay, the seller obviously wanted $101 for the item so it would make no difference to the buyer how the two parts of the transaction were divided.

With my BIN store items I have them all listed with free postage, the few cents extra in FVFs is worth the hassle saved having to justify my meagre one dollar P&H charge that I add onto my auction items lol.