Same problem here, the calculator made me lose many sales for over a month. Some customers were kind enough to let me know about it and wait while I fixed the listing from calculated to flat. Problem only effected US buyers.
eBay told me to do this and do that, nothing worked and now I had to change all my listings to show calculated for Canada and flat for USA... Oh well.. I can't afford to lose more sales and still pay listing fees on them!
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They are setting us up to fail
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"Hooked on Hookah!"
Mr.Shisha