@Nancy251
The two fees are handled in totally separate ways. The guest's fee is added to their booking. Your fee is taken from your earnings.
The booking fee is adjusted according to the length of the stay, and added to the overall total for the accommodation. So if your guest books for the full price (without any discount) the booking fee is based on that. If after that point you reduce the cost for the guest, the booking fee will be readjusted for the guest and they may get a refund.
Your 3% service fee is taken off the total that the guests will pay you - again that will be adjusted depending on the final price that the guest pays.
Unfortunately you won't be able to see a breakdown until the guest actually books.
Just wondering if there is an easier way to do this, which is to say to your guest that you will give an x% discount on the total that you will receive. They can book and then you will see how much you will earn and you can amend their price based on that.
Sorry I can't be more helpful...!