Is understandable that your actual business is based on older clients that are still stuck in fiat world. Is not even worth it the effort to start convincing those to user Bitcoin. You are right, charge an extra fee for paying in fiat. Fiat maxis will don't bother.

In time, I would recommend to promote your services to a broader spectrum of clients, where maybe you will find some bitcoiners willing to pay for your services in sats.

Or consider changing your activity if you really want to be paid in bitcoin.