So i actually found a simple way to do exactly what I was looking for using the bubble built plugin.
Have the seller register via connect in a separate process. The plugin supports this.
Have the seller put their item up for sale.
When the buyer goes to buy it you show them the cost + a surchage.
Using the bubble “pay via CC” process to have the buyer pay for the item.
Then create a new task called “transfer to seller”. This will now go to the sellers connected account. Set the charge ID to be the charge id of the previous task. And all the right things happen.