i have tried both when selling, i have now just put the postage calculator into it as when i was adding postage to my items i was getting it wrong too often and ending up out of pocket.

its fine if you know the amount your going to be charged but once you go over the basic 500grams, suddenly different postcodes are different costs and box sizes alter things. nope, just put the info into the calculator and if its wrong and they get overcharged just refund the extra.

its far from perfect but if its wrong at least i can blame ebay.

as a buyer i look at total cost not if there is free post. i see some sellers double listing the same item, one with postage one with free post but to 2 totals are the same. go figure that one out.