My policy is similar to that of phaZed. On those boards that don't power on after a jack replacement, I first verify my work. Assuming the new jack is doing it's job, I will then offer the customer a new quote along with at least a basic explanation. Many times the board is still repairable, but I don't throw this service in for free. If they decline, I charge them my diagnostic fee only. After many years of this, I have only ever had one unhappy customer (a teenager).
This was more common with the now "older" Gateway's (MA7, MA3).