Overcharged for postage by Royal Mail
As of late I've had 3 parcels arrive where royal mail have declared what I've shipped as wrong postage, not only that but it takes over a week everytime for the buyer to know. The parcels are 100% correct, I measure the size and check the weight but for some reason they tag it as wrong & I just have to pay. And as they've deleted their social media support account, all you can use is their webforms of which there's nothing for overpaying postage or ring them up and waiting forever.
I sell a lot on vinted and I know this is sacrilege to some but I've never had an issue with evri or inpost.