Is that a thing now? I didn't think you could charge fees on a delivery service, as it would eat into the funds for the service itself.... Which would mean you're getting royally F'ed if you're a seller.
I do believe if a seller lists something up for sale and the postage is a lot less than imagined, you shouldn't have to pay anything more than asked. If you ask for an additional service, i.e. insured & next day, instead of the slow boat from China, then you'll probably pay over the odds to get the service you asked for.
On the otherhand, if you think they're profiting from the delivery fees, I'd question them beforehand and just make sure you're being charged adequately. No one likes being ripped off.