if you accept jobs within a narrow margin of profit, for any length of time, there will be no business, and what if an un expected cost comes up, or a time delay, how will you adjust to that, a good GC will want strong subs, in good finincal condition

I agree. My former employer bids kind of slim, in order to get the work, with the hopes of getting a fatter margin, later. Even though this wasn't our disagreement and I never debated him on his estimating, I feel that if you bid the margin that makes your company solvent and provide value for what you charge, your reputation will help garner business, later. It does no good if you low-ball, get the contract, then can't afford to finish it. And I'm not saying we would have to charge for a small change order of moving a plug, or even adding one during rough-in. I could give away a couple as a good will gesture, especially if I'm making the margin that is comfortable. But if, as we're installing lights and someone wants a change the requires re-piping say 300 feet of pipe, I would have to charge for that. One of the GC supts I have dealt with brags about talking small contractors down from their original estimate, not because he really thinks they are over-charging but because he thinks it makes him look good to everyone else.

I worked with him last December when my employer was first starting. I was a W-9, sole proprietorship for the labor and did much of the work myself. And this GC Supt. was telling me I ought to make a little less an hour, to "help out others and help secure more jobs". I politely let him finish his spiel and changed the subject when convenient. According to my former employer, I ticked this guy off, even though I was polite and even-mannered with him, even as he would fly into emotional fits of rage.

Well, I can be polite but I don't "kiss butt". The best I can do is keep quiet. People will hire you if you are professional and worth what they pay you, though the "bottom line" has a big influence, too.