There are certainly risks involved. You would not be able to prove that you have no additional copy or backup of the prviate keys. Thus should you sell your wallet to me, I would transfer the coins ASAP. There would be no reason to complicate things, you could just directly send them to me.

Another problem I can think of is closely bitcointalk related. If I had your private keys I could sign a message with an address you posted in the past. I might be able to convince theymos that I am you and your account should be mine. There are possibly more thing I could do with control over your wallet.

Regarding that issue you could certainly post a signed message in said thread with a new address. Merely posting a new address might look like you are the hacker trying to secure the newly stolen account and I am you trying to regain access.

Something along the lines of:


Another possible problem with sellings the wallet.dat file might be a leak of privacy. Someone might learn a lot about you if they knew all of your addresses.

Think I'm missing something here, the obvious question: why would anyone buy any bitcoins this way?

There are some risks to the seller (as noted by Shorena) but buyer's risk of losing coins is huge (I recall some scams being done this way on newbies).

The only benefit I can see is if you're selling control over some rare vanity address.

If I'm the buyer I would be reluctant to participate in the trade. What guarantee would I have have, that in the event after paying you the money, you would not transfer out all the btc contained in the address since you also maintain a copy of the private key? It's still sounds more logical that in whatever scenario, it would still be best to use an escrow service. 

When I gave some BTC to my little cousin (less than one BTC actually), I created a wallet on blockchain.info for him. Then I gave him the wallet complete, explaining him how to use it, but I wouldn't do that to a stranger, nor would I accept a private key as a payment.

i don't see any problem in selling the entire wallet(just destroy all the backup of it, and possible private key of that wallet), you will then make another fresh one, see it as "one private key"

If you did that - there is a problem for the buyer in that you could potentially move the coins out of the wallet back to you faster than he can. If you already transferred the funds instead - there is absolutely no point in providing the private keys, unless you're trying to use it to fake verification or something. There isn't actually any real use to sharing keys since you cannot ensure that your funds are ever safe there.

Huh?
I am not sure what I read but...
Why would you do that?
What benefits would it have?

Also, even if Satoshi did that (which he didn't) what makes you think he didn't keep a backup of the wallet?
I am sure someone like Satoshi knows very well how important a wallet backup is.

So to close this,
I don't think that's what happened so do't worry your head about it. 

This could make sense under specific taxation regimes: In case the buyer lives in a jurisdiction that allows for tax-free profits after passing of a holding period, unmoved coins could be presented as evidence for holding the coins long enough. In that case, buyers might even be willing to pay a premium for unmoved coins.

Another motivation might be to cause identity confusion, by changing ownership "off-chain".

However that's mostly theoretical and I don't think it would be worth taking the risk.

ya.ya.yo!

Well how will I trust you didn't make a copy of the wallet and keys?
How can you prove to me that you didn't?

I don't know if there will be any any consequences, but I don't see the point in something like this.