Would you be also okay with the following situation: You have someone remodell your garden. He comes up with an estimate of 1 week worth of full-time work for two people. Based on your experience this seems reasonable and you agree on a fixed price of 10000$.
Two scenarios of what happens next: 1) He shows up the next day with a gardening robot you never knew existed and he never told you he would use. The work is done in 30 minutes. He goes home to spend time with his kids. (Or maybe contract more "2 week projects"?)
2) Two gardening people show up every morning to greet you when you drive to work. They leave when you come back and make steady progress every day. On the last day you come home early and witness that actually the daily work is done by a gardening robot in 5 minutes and the two people actually drive home during the day to spend time with their kids.
Would you contract this guy again?