Can I refund and refuse to post an item if I can't dismantle it?

[Whitty]

I sold a big toy that I thought would dismantly easily to go into the box to post, but it just won't budge!
Can i refund, and email to explain that I will have to relist for locals only?

Ooops, posted twice thats weird, told me first time it was blank.....

If I was the winner I'd be OK with that. I'd be disappointed, obviously, but anyone with an ounce of reason would understand. Just be apologetic in the email!