2. 13. 1 The right to choose the serve, receive and position shall be decided by drawing lots. The winner can choose to serve or receive the service first, or he can choose to be in a certain position first.
So in the standard procedure, it should be a coin toss to see which side guesses the lottery.
In operation, the referee should pay attention to the angle and height of throwing, and there should be no suspicion of manipulating which side is up, and there should be no palm flip when receiving the service.
This should be said to be fair.