Did it bounce twice?
A ball must be returned before it bounces on the floor a second time. Walls and mesh in between do not reset the count: two bounces on the floor and the point is lost.
The rule
After a ball bounces in your half, you have until its second bounce on the ground to return it. It may hit the glass or the mesh any number of times in between, but only the floor counts as a bounce.
The close ones
Balls that die off the glass, low drop shots and balls scraped up off the floor are where the second bounce gets argued about. The player playing the ball is usually best placed to know.
Calling it fairly
Without an umpire, the rules do not say who calls a double bounce. Good practice is that the player who played the ball calls it on themselves, straight away, and that when the four of you cannot agree, you replay the point.
Questions
Does the wall count as a bounce in padel?
No. Only the floor counts. The ball can hit the glass and the mesh and still be played until it bounces on the floor a second time.
Who calls a double bounce in padel?
In a refereed match, the umpire. In social play it is usually the player who played the ball, and an honest replay settles real doubt.