Use a Tax

The fee charged by the marketplace does not change the invoice amount, using a tax does. Would this work as a commission?

Set up a tax authority as "Tax Included in price"

Doing that, has the effect of reducing revenue, rather than increasing cost. The gross profit is the same, but according to ASPE accounting standards cost should be increased, rather than revenue reduced.

We're had this come up a few times before Aaron.  I can get someone from our team to speak to you for a few minutes if you'd like.  

[email protected] 

We do something similar where sometimes we need to push a cost to a sales order without charging more "price" to the customer.  Situations like assigning an extra freight or handling cost to a customer if the freight bill didn't get built into the cost of goods.

We use an item number that is not a "stock item".  And set the account set to a "user defined costing".  This allows the item to be added to the order at a zero price, but you can manually change the cost.   You would have to have the item setup properly ahead of time so that it uses the correct GL codes, but that's how we do it.  

We also use this system for tracking vendor rebates to customers.  You can use this system on the credit side to not give a payment reducing credit, only a cost reduction to the customer account.

Hope that helps.  Obviously this would be a case-by-case basis so not sure if you are trying to setup a more automated approach