The most valuable examples of the Commodore 64, generally speaking, are the early variants that have silver labels across the top. The silver label Commodore 64 is the earliest, most expensive example of the venerable machine.
In all, Commodore produced about 80,000 of these machines. That compares to several million of the most common variants. That alone makes them relatively rare. When you do find one, there’s a fairly good chance it’s not 100% original.