"When they used up all the cooling agent within a month, after it being freshly charged" Freon is not used up, it disappears when there is a leak. Your HVAC tech determined it was from their misuse? Really? The A/C unit would stop running if the Freon was low due to a leak by the low pressure switch. Same with running too long, the high pressure switch would shut it off. It seems improvable that a judge would award $700.00 repair bill on an old A/C unit to start with! How would one prove misuse if all one did was run the A/C unit?