Sounds like he's trying for a five-finger discount.

Don't blink. If it's through Paypal, I bet London to a brick, he will have to pay postage for the return, as you have Paypal proof of postage. Unless he knows about the Paypal free returns. Hint: don't tell him.

IF you receive it back, still in the original condition, reassess from there. Londons and bricks again, the package has been opened. Likely he decided as a pensioner he is entitled to rip people off.

Not knowing their circumstances.

If he knows enough to trade on-line, he should have at least a working knowledge of photography. It's been around for more than 100 years.

Edit: If it was for his kid's birthday, surely the packaging is irrelevant. Unless the kid is an adult collector of 'new in original package' slot cars. Which is possible, but the onus is still on him, especially through Paypal, to return for a refund.