If a buyer sorts a courier who is liable if the item goes missing

[m25jet]

It's not advisable to arange for couriers to collect an item on your behalf if you've committed to buying it or have won it in an auction, as with Collection In Person Only listings the onus is on the buyer to collect the item personally from the seller.  At that point the buyer would then have the chance to check the item over, and if it subsequently became clear that the item was not as described the buyer couuld then tell the seller "I've changed my mind - I don't want the item now" and walk away from the sale, still with the cash in his/her pocket.  Alternatively if the buyer is happy with the item he/she can then pay the seller and take the item home with him/her.

In the event that the buyer gets somebody else to collect the item on his/her behalf then the buyer will have voided his/her buyer protection in relation to that transaction.  Therefore, if something went wrong when the item was collected - for example, if the item was damaged, lost or stolen in transit, then if the buyer tried to bring a case against the seller eBay would decide the matter in the seller's favour due to the fact that the buyer had voided his/her eBay buyer protection by getting somebody else to collect the item on his/her behalf.