Do you charge differently when a "fill-in" client shows up with almost nothing left?

Fill-ins are supposed to be quick touch-ups, but sometimes the client shows up with barely any product/result remaining, and it basically turns into a full redo. Is the usual move to just eat it and charge the fill-in price anyway, or does it make sense to have a policy for switching to full-service pricing on the spot?

Would be good to hear how others handle it without it turning into an awkward negotiation every time.