I don't consider it professional either. I mow two homes on that same street and I've considered going to the door and talking to the people but I hate to to do that because I don't want it to seem like I'm trying to cut the guys throat but at the same time it's this type of lawncare company that's giving the business a bad name. That home has a 3/4 to 1 acre lot and he mowed the whole thing in less time that it took me to mow the front yard across the street.
This is a tough call but I think the right thing to do is go and knock on the door.
Maybe the homeowner is not really happy with the job he is doing and likes how your doing the yard across the road. But thinking you might cost to much more than they are paying him. I bet you both charge close to the same.
Do I think that it is wrong for you to take this yard from him ? NO he needs to learn if he wants to keep his yards he needs to step up the quality of his work.
You and I disagree a lot but I do believe you take some pride in your work
(( racing is the only sport that you need two balls ))