It was never difficult to play CS for free, and that's probably the reason for its success. I remember getting into CS because you could play online with basically any Half-life product key and by 2000 you could buy bundles that came with like 3-4 keys.
I think CS, in that era, was free if you had a HL product key. It was a community mod and even when it transitioned to a boxed standalone product you could still download it if you had a HL key. CS: Source was also a free upgrade.
