I can make you a interface where you can add "Client number" and "Your Seller Number" and switch it on and off.
If it is on, the messages you receive from client will be sent to the seller and vice versa.
For this to work for your benefit , you need to tell your Seller to not to talk some stuff directly ( money related ) .
I can stop sending the messages having words like "money" ,"bucks" ,"dollar" ,"$", etc.
You need to have an active internet connection as this will be using Whatsapp Web