I have one that is a huge pain to mow. It's 90% hilly and broken into multiple, irregularly shaped sections by flowerbeds.
I underbid it because I was inexperienced at quoting. I trudged through the first season and thought about dropping them this year (because I know they will not pay more), but after having purchased a walk behind, I was able to complete it a little more quickly, and decided to "keep" them.
The property is in a semi-wealthy area on a heavily traveled "shortcut" side road and there are a lot of local dog-walkers that see my truck and my lawn signs. (placed out while mowing) The exposure is the only reason I'm still there.
That said, I've decided to drop them next season. I've picked up other accounts nearby and can now get "exposure" while being paid what I should be paid.