People expect you to work for free because you have done work for them.
I had one customer that asked: "is there a 6 or 3 months grace period after the panel upgrade"
ME: What do you mean?
Customer: You can change fixtures and switches?
ME: Well, there is no grace period. When ever you are ready i can change them for you. But of course there is a charge.
Customer: OHH. I thought there was a grace period with this panel upgrade.
ME: Seriously, you thought i will change fixtures and switches for free?