Is there a way to charge a customer a flat fee for a service in a Sales Orders (not in the Service area) without using a resource (don't want to track units or cost), something like an Item Charge, but wouldn't need to be associated/assigned with an item in the Sales Order as an Item Charge would require.
I was thinking of creating a Nonstock Item, but I am not sure if this is the way to go. This is not a tangible item, it is for a service, and we are not concerned about tracking costs in relation to this fee (if wanted cost info we would use the service area as we already do for the repair people in the organization).
Yes. You can use the invoice discount function for this. Here you can even use it to specify a min. amount to avoid the fee.
The Invoice Discount Code on the Customer to specify different levels.