Antifreeze recommendations for a Smart 453?

Curious minds want to know:
How do you know you are using the "wrong coolant"?
Any telltale sign?
What can go wrong if you are mixing in the "wrong coolant"?
E.g. top up the coolant level but have no idea what the existing coolant type/brand is?

I suppose that is why they can sell the "OEM replacement coolant" for 5x the price of some "generic coolant"...
Since my 453 is using a Renault engine, I would lean toward the cheaper "generic coolant".
Note: I am not an engine coolant expert. It is just a personal preference.