Can a lawn care contractor charge both a flat-rate plus an hourly rate (time and material) for the same job without a contract?
They are free to charge however they wish so long as it makes sense and is lawful. For example, they might charge a flat rate for X, Y and Z, but an hourly rate for all other services.
If you feel that you are not being treated fairly, I suggest that you consult with a lawyer in private and discuss your situation in more detail. You can start by calling around to several for a free phone consultation, get some insights then pick the best fit to work with.
Best regards,
Frank
Natoli-Legal, LLC