Paying cash on pick up items is better for both buyer and seller.
If you only want to pay cash and inspect the item first, then you are well within your rights to ask for a cancellation.
If you are going to pay PayPal then seller will need to send another invoice to reset checkout so you can pay.
Personally if I buy a pick up item, I want to see it before I pay then I can walk away if it is not as described.