I think you should warn the users about the risk behind getting this address and private keys, since there are more people who have a copy of those private keys, then the users who buy this will risk their money if they decide to send coins to those addresses.
If the goal is only to use those addresses to sign messages, then there is not a big deal, but people must know how these addresses are a high risk for the funds.
These addresses were unused which received a specific 'signature chain', they contain some sats to transfer the 'signature chain' to the buyers own address. The items exist only 1/1, so nobody else can buy it after purchase. Only one buyer will have the private keys. I have the private keys too, but it is the same situation like coin-mixer. The mixer has the private keys of the new addresses too.
Yes, I will edit the 1st post that the new owners shouldn't use these addresses for their own transactions.