Multi Family real value

[Account Closed]

Good evening to all experts. 

I have a question regarding the value after a Single Family has been converted in a Multi Family. It now is a a 4 unit studio.

The value of this property from the tax county is 29000 $ and the resale price is 60000 $. Is the tax county assesment always accurate or is it the fact that with the yield increase (due to the multiple tenants (4)) and the conversion works owner can resell at a higher price ? 

Sorry my english is not great I am a overseas investor.

Thanks for your reply (if you understand my question)