I get that the postage price is clearly listed, but I don't think the buyer is the cheeky one here. There are so many different postal charging structures now from all kinds of retailers/sellers, depending on volume, carrier, special deals etc., that it's no longer a simple thing to reconcile in your mind as to what it 'should' cost to send a particular item.
It's complicated further when some companies have a flat postage fee, on which they might make a profit if you don't order much (although still the same admin for them for a lower-price sale, of course) and/or they charge it based on order value - so you could end up paying less for some cheap hardback books than for several sheets of premium stickers.
I'm surprised at the responses here. Yes, you shouldn't profit, but the COST of posting isn't just the stamp. It's the packaging, the time to wrap it, the fuel to get to the post office (and maybe parking) and time to do so. It's 'postage and packing'. Yes, be reasonable, and don't charge £10 postage for something that costs £1 in stamps, but the cost should be more than you see on the postage label when it arrives.
I agree with this to an extent - it's postage AND packing; shipping AND handling, so you shouldn't be out of pocket - but equally, it isn't your buyer's issue if you live in a Highland village and have to pay for a taxi 15 miles to the post office and back again in order to post it.
People profiting on the postage has become a vicious circle, really, as eBay got wise to people selling something suspiciously cheaply but with an eye-watering postage charge, so as to reduce their eBay seller fees, so they then started to levy the seller fees on the total of the amount you ask the buyer to pay, including postage. This solved the issue and thwarted the high-postage profiteers, but also then meant that honest buyers have to charge extra postage to cover the cut that eBay takes or otherwise make a loss.
Realistically, I think separate postage costs are going to become a thing of the past. Rather than making your item look cheaper, it actually tends to make it look dearer, even if the total is still less than the all-in price that a competitor is charging for the same item with 'free' postage.
Now that online shopping is no longer a niche way of buying things you simply can't find at normal shops, but many people's automatic go-to method (accelerated even further with lockdown and other COVID restrictions), I believe that charging separately for postage is looking more and more anachronistic - heading the same way as the old fees that used to be routinely charged to customers paying for goods by card (sometimes even when there was literally no alternative method).
If I buy something in an actual bricks-and-mortar shop, I couldn't care less how much they need to make on the sale to cover all of their electricity/lighting/heating bills, banking/transaction fees, other overheads, staff costs and profit, not to mention the VAT that they have to collect on behalf of the government. Figuring all of that out is their job, as it's their business, not mine. I just want to be told an all-inclusive price that I can pay to them in exchange for becoming the new owner of the goods, and walking away with them, so that I can decide whether or not to make the purchase. As I can't collect most things bought online myself, they also need to figure in the cost of getting the item(s) to my door in the total price they quote me.