The internet is in many ways still in it's infancy with respect to the law. With that said, your question is not necessarily on of legality (as I am unaware of any crime the would be committed by online auction) but more about basic tenets of contract formation. The biggest potential issue I can imagine is the enforceability of the auction. A competent attorney can help you sort out these issues and ensure that you're risk is minimized.
Always consult with an Attorney before taking any course of action with respect to a legal matter. I provide the above communication for general informational purposes only. This transmission and any subsequent transmission from Dennis E. Sawan, Esq through Avvo, is not intended as legal advice and no Attorney-Client relationship is meant to be established.