How do you price a complete system replacement vs. a repair on borderline calls?

Talking specifically about the gray-area calls. 12-year-old R-410A system, evap leak, not under warranty. Customer asks “”should I just replace?””

What’s your decision tree? At what point do you stop pitching repair and pitch replacement? And how do you price the repair side so it’s worth it for you AND honest for the customer?

(Owners feel free to weigh in, this isn’t just a tech question.)