Did he know it was an expensive item?

Maybe you can sell NFTs of the bicycle since you don't own it anymore. While there are a lot of assholes who pay thousands for old junk, there are similar numbers who will throw real money at NFTs.

Kind of fucked up that he wouldn’t check with you, the owner, about items that weren’t his. I suggest he try reaching out to the buyer to buy it back. Chances are the buyer won’t know the value either and will return it if you just talk about the sentimental value of it being in your family. Good luck.

So, smack the shit out of him?

Tell your husband to give you the customer's contact info. Tell the customer that bike wasn't his to sell, you need it back, and a refund will be issued.

I would have sold that Xbox.