yes I remember well, like The Last Ninja 1 or Way Of The Exploding Fist on C64 tape, were damn hard to copy on an audio deck, you had to use these chrome tapes as target tape, normal tapes would not work as a copy. But I believe I hacked the latter game, it got it transferred somehow on disk and made a new loader that made it run straight from disk, I remember I was so proud
And it often required a damn good dual audio deck too.
Finally, a screwdriver was also needed to adjust the heads to make it work for certain games!!
If the copy was bad, the game would never start/load forever until it ran out of tape.
But my dad had a colleague at work who made a lot of homebrewn hardware for the C64 and he made me a sort of dongle where you had to connect 2 C64 datatapedrives, it had a led, a L/R switch to indicate what was play and what was record deck, and some other cable that went into the C64 tape connector. That copied all commercial tapes perfectly, but only at normal speed