It all depends on the deal you made. If you both agreed to do *** for *** amount of $$$ and you went further without getting another agreement to go ahead to do *** for additional $$$ I think it very could be a problem. I would be really unhappy if someone was spending $$$ I might not have without asking first. He may have a limit on what he wants to or can afford to spend on this project. The big thing is commmunication, communication, communication. He may be able and willing to kick in more money.
I don't agree with you on this one and it sure isn't the way to make friends but is a sure way to kill any future business or cars that he may send his way. Your word is your reputation.
I know you are a fair person from what we have dealt on. Stop where you are and negotiate any additional work that needs to be done but hasn't been done that wasn't part of the original deal. If he doesn't want to go any further past what you have agreed on then only do what you have agreed to do and eat what you did without an agreement.
None of us want to work for nothing and believe me I have made deals where I have lost money to do a job. Did I like it, heck no? Most of the time but not always, it came back in referals that I did make some good money on. One of those deals was on a mattress contract that I lost just over $5.00 in real money besides my labor on every mattress I did on a contract for Oklahoma State University. That cost me over a $1000.00 in real money plus all my labor. Soon after I was handed an open ended contract from them for $2483.90 a month for rebuilding their box springs so I ended up with an almost $30K a year contract that I made big bank on.