Hi, does anyone know what the real-world consequences are of

A C/2 is not a house - as you know.  So you would be living in a garage come deposit.  This means that any work done will have had no permissions - the 'house' can have no kitchen or bathroom - and cannot have agibilità, can never be sold, and you can be prosecuted for doing works without a building concession.  Basically it means that you are living in an 'abusivo' building and it can be sequestered.    You wont be paying TARI, and that means you can be prosecuted.   You cant buy a C2 and get prima casa agevolazione or any other incentive.   It cannot be rented out, either long term or as a holiday home.  It may not have the prerequisites for a house, and therefore is technically uninhabitable and you can receive an enforcement notice to quit.  

If you are thinking of buying a C2 to live in, dont - it cannot be sold without making false statements in a public act and making your act of sale null.   You cannot take residence in a C2.  While nobody can stop you sleeping in a garage, it will never be a house.  You can not sell it as house - and if an agency is trying to do so, it is a crime.