Can i bill a customer and reduce the amount owed by adding a broker fee?

Yes, you can add a broker fee to your invoice, gofertrucking-ya.

First, you need to create a service item for the fee, then add it as another line item to the invoice. 

Here's how:

1. Click Sales, then choose Products and Services.
2. Select New, choose Service.
3. In the Product/Service information section, enter Broker Fee under the Name section.
4. Under Income account, select the expense account that tracks the broker fee.
5. Click Save and Close.
6. Hit Save and close.

If you haven't created an account, follow this link to for instructions: Add an account to your chart of accounts in QuickBooks Online.

After that, here how to create an invoice and enter the broker fee as a negative amount:

1. Click the Plus (+) icon, then choose Invoice.
2. Select the customer's name,
3. Under Product/Service, select the income account and enter the amount on the first line.
4. On the second line, select Broker Fee and enter the amount as negative.
5. Click Save and close.

Once you receive the invoice payment, you can record it. Please browse this article for instructions and detailed steps: Record invoice payments in QuickBooks Online.

Stay in touch with me if there's anything else you need help with managing customer's transactions. I'll be around to provide steps and articles.