What you really want to look at is the condition of the motor, look for corrosion and check the compression, if its within 10 psi for each cylinder that is good and you want it close to the normal compression, if there is an issue use DUNKS Sea Foam decarb method and then check the compression.
If the motor has 1500 or more hours on it then use that to negotiate the price.
If the motor has 1500 or more hours on it then use that to negotiate the price.