It is a fair value only if you feel comfortable paying for it, and able to pay for it.
here we go,
You will get 80% of the value of the OMV when the car reaches 10 year old and scraped. That will be $16,000.
$50,000 minus $16,000 = $34,000
Now you must know exactly how long is left for the car's life (in months or years). Assuming 5 years exactly, then the depreciation per year will be $34,000 divided by 5 = $6800. Which is a reasonable industry standard for Toyota cars.
Different brand will have different depreciation values. Same brand but different models will have very little difference in their depreciation.
One way to beat the vendors to their own game is to check the classified ads in the newspapers for those car dealers who want to buy cars from you. Call them and tell them you have a particular car for sale. Give them the brand, model and month/year registered, nothing more nothing less because the vendor are not interested in other aspects of your car, e.g condition, accident free, paint work, new bumper, leather seats etc. They will give you a quote immediately over the phone. Then they will say "If you agree to the price, I will come down NOW to see your car".
The quote they give will always be $10,000 less than what they finally sell it to others. Of course they will respray the car, vacuum, do up the interior, spray in your engine bay (armour), oil the tyres, do all the paperwork for the transactions and loans, etc.
Is it worth the $10,000 premium if you could have just bought the same car off from a genuine car owner.
You decide for yourself.