If a kid on my street asked me to trade with him and I was interested in doing it, I would approach the parents and do the deal through them. That way I would know for sure that it is OK with them for their kid to have the item and also that the terms of the deal are OK with them. In this way, it would be you giving a knife to an adult and the adult giving the knife to their child. Nobody can ever come back to you later and ask you, "Why in the world did you give that knife to a kid?" That should also limit your potential liability if something bad happens with the knife. This just seems like common sense and maybe it could be applied to an internet transaction as well.
As stated above, this kind of transaction is technically a contract even when no formal written contract exists, so refusing to enter into a contract with a minor is justified based on the fact that you cannot enforce a contract against a minor. If you do it, you should be sure to receive payment in advance.
As stated above, this kind of transaction is technically a contract even when no formal written contract exists, so refusing to enter into a contract with a minor is justified based on the fact that you cannot enforce a contract against a minor. If you do it, you should be sure to receive payment in advance.