Reply to DJing with sync, mixing in/handover

So if you did not know how to beatmatch and relied on sync. How do you mix into the previous DJ?

It has only occurred to me recently after all these years that if you rocked up with your controller and only knew how to press the sync button to beatmatch you could not flawlessly mix into the last tune.

Unless you at least knew some rudimentary basics of beatmatching.

So I am a bit confused on how all these DJ's who rely on sync do this?