Overheating problem

just purchased a 1997 mercedes E320. mechanic (niece’s father) changed the fan (AC & engine) and belt which he said needed to be done. Now the car is oerheating and he wants to replace the fan clutch and the thermostat. I am so despondent and dont know what to do. car was running good prior to the repairs now its laboring. 124347 mileage and in excellent condition. i need adice