To answer my own question,to give others the info if needed. It wasn't clear using Send It Now how to use the drop and collect from a PO. What I have done is picked the nearest PO to the seller (from whom I need a bike collecting) and then the buyer (me) to have it dropped off at. The seller has dropped the bike off at the PO and they've accepted it, job done. Only issue I may have was the weight. The site gives a 30Kg limit when using the courier to collect and drop off, but this is reduced to 20Kg when using the PO. I put the weight of the bike I'm getting in at 15Kg as a guess, PO weighed it and got 24Kg...so I may be charged when I collect.