As a seller, you can accept multiple offers on a single listing if you have more than one of that item in stock!
As long as the item has not been marked as sold or reserved, it will still be available in the marketplace for other Carousellers to search, view and start chats on.
However, if you only have one of the items in stock, it is not encouraged to accept multiple offers as the acceptance of an offer is irreversible and signifies a commitment to deal. Once an offer has been made and accepted, both parties will be able to leave feedback for each other.
Accepting a single offer would be ideal in this case, as accepting multiple offers would mean that multiple unhappy buyers will be able to leave feedback on your profile if they wish to.