I have a live listing and have allowed potential buyers to make offers. However, I have an e-Bay account holder who has messaged me directly, offering to buy the item at a stated price and that I should make an offer back to them at that price, which they would accept. 

Is this a risk to me? I don't understand why they would not simply select the option on the listing to offer me the amount they are proposing.

It is quite an expensive item and I am wary of any possible scam attempt.