Anyhow, I asked the customer what they did and he said he did not do anything and happily send me the payment with taxes and shipping difference. So it must be one of those eBay glitches.
With competing marketplaces popping up all over the globe, I wonder how long will eBay buggy platform stand against better-writen competitors once they get to some serious trqaffic. eBay is like "Yahoo" of internet commerce, with bloated website and living off old fame. I wonder who will be "Google" of internet commerce taking it by storm with well thought algorithms and simple and working website ... 😉