The buyer will go through checkout if they are paying with Paypal, when they do they will confirm the address you need to send to. always check that the address is the same as on the Paypal transaction page as that may be different fronm the email you received fron ebay when the item sold.

If it is for the trainers and they went for fifty bucks or close then you should send by registered post or click & send, ordinary red or express satchels do not have tracking that qualifies for Paypal seller protection.