we have taken care of a school district for 2 years now. Never had a lick of problem with them. Before us they had hs kids working off their tuition (private school) and obviously this was not much of a motivation and the grounds looked awful. We offered to clean up everything for free (over 20 hours worth of free labor) and get everything looking good then offered a per mowing price. They took it. This past winter they talked about bidding it out - and decided not to b/c they were happy. It may seem insane to offer free clean-up, but i knew that would be the hook if i could just mow for them once. I also kind of feel like I am giving back since it is a Christian school - so it all works out. I will increase my prices ever so slightly this year - I didnt last year for them. Good luck.
(keep in mind that this is a private school, so your experience may be completely different)
(keep in mind that this is a private school, so your experience may be completely different)