Not sure but you often see 'P&P not included' when ads offer XX days trial period and refund if not suitable. Where the return is because the item is faulty I have found that companies that I have dealt with usually arrange the return. In fact I had reason to return an item just this week to Westfalia and I called them and they arranged for collection by Parcel Force the very next day. I didn't even have to label the parcel, the driver had a preprinted label to stick on it.
QVC for instance, don't pay the return cost or refund original postage if you just don't want the product but in the case of a faulty product they will send you a pre-paid label.