Lets see
Item $20 postage Free Total $20  Ebay laughing all the way to the bank, and will never increases shop prices again.
Item $19 postage $1  Total $20   Greatest seller since sliced bread with 100 & 1000s
Item $18 postage $2  Total $20   Greatest seller since sliced bread
Item $15 postage $5  Total $20   Just OK seller
Item $10 postage $10  Total $20   Scammer wreck his business
Item $1 postage $19  Total $20   Total Rip off scammer lets wreck his business low stars and neg public flogging too good for them

Same item same total costs, if you dont like the deal or the postage or the font the seller uses, its easy DON’T BID.  If you think the postage is too high DON’T BID, if you are unsure about the postage ask, communicate, if you don’t like the answer then DON’T BID.  Concerned about only getting $1 back in a dispute as rest is postage Easy DON'T BID

As for some buyers not knowing what the postage cost is so what? Makes no difference to the final total.  You do not how much the buyer paid for the item either but you dont care. So its OK if seller sources an item for free has postage of $3.80 and sells it free post for $20 a 425% markup but totally unacceptable to charge $10 on $3.80 postage (markup 160%) ignoring the cost of packaging and time taken to deliver to letter box or PO.  Seller made $6.20 on postage ignoring other costs probable min time taken was 15 min with delivery etc so he made $24.80/hr.  Watch out Gina your spot as Australia's Richest is in danger.

How did he rip off anybody the cost of postage was clearly displayed for all bidders to see, further he charged exactly what he said he would.  If he had wanted more for post or the item or it wasn't in the condition described then thats a ripoff.