I always contact my buyers around day 5 of non collection as I have found that sometimes they don't get carded.  AP issues a "Final Notice" to collect on day 8 which can be too late.  If they then fail to collect and it is returned I would only refund purchase price as you posted item in good faith and it was their decision not to arrange collection.  They also could have contacted AP and arranged for parcel to be forwarded to another PO for collection say near where they work.  Most large POs have an early collection area where you can collect from 7AM usually located at side or back of PO with a buzzer to ring.