I should be clear, since the quote might be taken out of context due to the bolding.   I would tell them that if they can't pay, it's perfectly fine. In addition, I'd give them a deadline before I would relist. Looking at it now, it might seem a little pushy to give a deadline but this would only happen if they hadn't contacted me after the initial message to ask if everything is alright re: payment. I've done this with a buyer and it all worked out.

The problem is . . . . if you do not do a mutual cancellation OR UnPaid Item claim and you relist then the original buyer can pay and expect you to send (even if you relist and sell to someone else).

Imagine this extreme situation . . . . a buyer does not pay . . . . you give them a deadline before which you will relist (say 10 days) . . . . buyer does not pay by the deadline so you relist . . . . . someone else buys and when they receive the item they leave you glowing +ve feedback . . . . then . . . . . ten more days later the original buyer pays by PayPal and asks "when will you send my item?" . . . . you reply with "but my deadline passed and I sold to someone else" . . . . then the original buyer leaves neg feedback stating "seller sold my won item to someone, not a good seller"  AND eBay will not remove the negative.

Actually, it is not such an extreme situation . . . . some buyers are just slow to pay when they are not confronted with an assertive seller who follows rules/policy.