I've just had to return a parcel as the wrong item was sent and the company said I had to pay postage and they'd reimburse.
The lady at the post office said I could send it for one price or if I wanted guaranteed delivery I could pay an extra couple of pounds. Apparently the lower price meant they may or may not deliver it but the higher price meant they'd (hopefully) be sure to. She said the fact it was quite a large heavy parcel meant they'd be more likely to lose it if I didn't send it guaranteed. 
AIBU to think that you should not have to pay extra to be sure that Parcel Force will actually deliver the parcel rather than that they MIGHT deliver it?