Well ....
There are not a lot of moderators to go around.
And we would rather not be involved in legitimate transactions, because we really don't need your private shipping and financial information.
If the Conversation is initiated by the potential seller, they control whether or not another party can be added to the Conversation. So you would need to start another Conversation yourself, and ad them and us.
All that being said, if you need our help, and can be patient with time differences and availability, I'd be unlikely to refuse.