I have two GC's that I do work for (all other business is with owner's). GC#1 is constantly on the prowl for the just-started-his-own-electrical-contracting-shop-and-doesn't-understand-his-costs-yet guy. I have been doing work for him for over three years and thru the superintendant's I have heard of several other EC's that have done work for this GC. They usually don't stay long. Probably because this GC drags his heels when it comes to payments. I keep him on a very short leash when it comes to money.
One time he called and said, "We got that kitchen remodel job but I had to throw in three extra recessed lights in the kitchen for free."
I said, "OK, I'll send over the change order."
He said, "But I didn't charge the customer for them."
How generous of you to offer my work for FREE !!!! He got billed, not full cost and we wound up not installing them anyway.
The second GC doesn't screw around. He's been around long enough to appreciate good work. He calls, we move. When we invoice him we get paid fast. I have done a few service calls for him for free. One time the elevator stopped working. The elevator tech comes out, meters the panel and says, "Your 3pole shunt trip 100amp C/B is defective. You need an electrician to replace it." Now, this C/B is only a couple years old so I meter the panel. Turns out he lost a phase coming in from the service gear. Long story short, I replaced a 1/4x20 bolt in the service gear and fixed the problem. A lot cheaper than a new breaker!!!
So the second GC doesn't even bother bidding out the electrical on his projects. In fact, we're doing the electric on his new house.
So, IMO, a good customer will warrant some favors from me. Those who try and cut pennies in half get nothing.
A mason contractor once told me, "Don't be a pig because all pigs eventually get slaughtered."