What makes a draw "prearranged"?
There has to be convincing evidence that the draw was agreed before the game. When the two players play nonsense moves and then agree a draw that is prima facie evidence that should raise suspicion but is not completely conclusive. More evidence is needed to justify awarding 0F-0F.
I know of two recent cases, one at a very high level and one at a low level, where this happened.
The very high level case is the (in)famous Dubov - Nepomniachtchi "Dance of the Knights". Although the moves themselves were highly suspicious it was the ChessBase India video of them prearranging the draw which proved conclusive.
The low level case occurred in the last round of the Isle of Man Major/Minor. Halfway down the field two players played 1. e3 e6 2. Ke2 Ke7 3. Qe1 Qe8 4. Kd1 Kd8 - draw. Unfortunately the arbiter came along as they were completing the game and tried to replace the kings and queens on their original squares. They explained that no, they had each moved their highnesses to their new squares and were agreeing a draw. After checking the scoresheets the puzzled arbiter decided to refer the case to the chief arbiter of the main GM tournament. He interviewed the two players who admitted that the game had been prearranged.
I have played in several tournaments where I have seen the tournament leader in the last round play a few moves before offering his or her (I've seen cases of both) lower rated opponent a draw allowing them to pocket the prize money before catching an early train or plane home. There is no good reason why these examples should be prearranged.
Similarly there are several top level siblings who usually play out standard draws when they have to play each other. These may be mildly suspicious but as long as none of the moves are nonsensical there is no grounds for further action.
