When you ask someone for an "estimate", as you did, that's what you get, an ESTIMATE!!
Maybe he thought he was going to hit rocks, stumps or who knows what. If he hit a 6' diameter boulder and it took 8 hours, would he get paid more than his estimate?
Did he hold a .357 to your head and make you accept his estimate? You should have asked him to work by the hour if you wanted to pay for exactly what you wanted, but then you might be back here complaining that he worked really slow and took a lot of breaks???
I understand your frustrations, but I'm sure you're a big boy and understand that when you run machinery for people (like I do) for a living, sometimes you finish sooner, sometimes it takes you longer. Hopefully it all evens out in the end. I can tell you that if someone is willing to trailer a backhoe to your house and do just about ANY trench for $400, that's not all that bad. It probably took him >1 hour to load the machine, binder it down, unload at your place 1.5 hrs to dig your trench, than >1 hour to load machine and take it home.
If he estimated it planning on hitting rocks or some tough stuff, but then he didn't, then it is screw the customer time? Seems so. If he would have hit a big rock shelf he would have charged for extra time anyway, and of course he should be compensated.
Certainly I understand it is an estimate, but it gets frustrating when the homeowner gets shafted both ways. When it is in the contractors favor, they hold the line at the estimate, but when it is in the homeowners favor, whoops we need more money.
That is not just operators in general. I find that in contracting out building jobs for houses and remodel jobs all the time. Maybe the estimators need to go take a class on estimating. I guess getting a few estimates is the way to go, but that still isn't a guarantee.
I had an estimate for a mound system 20 years ago from 4 plumbers. The cheapest was $6000, the next was a few hundred extra and so on. I couldn't get them in so I waited until the next April. I was building the house by myself and my wife so me had to get an early start in the year on it. I went back to the cheap plumber to give me an update because I expected prices to change. It shouldn't have been a problem. Mind you it took about 6 weeks to get the paperwork through the state so time was critical for me and he knew it. I waited 3 weeks or so and went to his place, and I got an excuse, "I'll was just going to start it." I waited another 3 weeks and checked the progress, "Whoops, I was just going to get started this week on it." Okay I said. Finally I say him in his truck someplace and told him to get with it a little bit. "Okay, I'll get right on it right away. Finally a couple weeks I went to his place of work and he said, "I have a new estimate of $9000. I asked him why so high. He told me the price of PVC went up and so did sand. I took him at his word and told him I'll have to get back with him because now it is July sometime. I called the next highest original bidder and he told me right away his estimate would go up about $400. I asked him how quick he could get the permit and he said he would walk it through the state but would maybe take a day or two so I told him to get going with it.
The first contractor knew I would have to get him if I didn't want to blow a year waiting for another plumber, and I was beyond patient and always am with all contractors. But, I remember little tidbits like that every time I get an estimate and have to deal with contractors or mechanics of any sort. But, I do let my guard down now and then especially when I know the guy. I learn all kinds of lessons that way. Maybe that's why I am so overworked. I get an estimate that is way to high or to slow so I just do it myself and get it done in half the time and twice as cheap. Homeowner beware, I guess is my new motto.