There are also dimension issues that come into play. When I flew a domestic leg from Vancouver to LA last year with a Coroplast bike box that I bought in Australia, claiming to be as used by the Australian Olympic team, it was measured at the counter, and was several inches oversize. The box was in this case my one piece of checked luggage and would have been free.

I got away with it being free because I was early, and smiled and was nice to the clerk, and pointed out gently that Qantas had flown it to LA for free, as had her airline to Vancouver.

Those big boxes would, on some airlines, attract a charge automatically because they are well oversize.

In the end, though, you are in the hands of the check-in clerk, irrespective of precedent, printed-out conditions, and any other paraphenalia or arguments you might bring with you.