Revealing mistake: When David pushes the pallets onto the car, it's obvious that there is no-one inside. Similarly, when he uses the forklift to pick up the car a few shots later, we see inside the car and there is only a badly constructed dummy-type object in the back seat, and no real people. Even if they had bent down, they should still be visible.
Audio problem: David doesn't like the Japanese song playing on the tape player, so he ejects it. When Kazuo comes back, he puts it back in, but the song doesn't start at the same place that it ended. Also, when Kazuo finds the damaged tape later, he throws it out the window, but when the van drives away, the tape is nowhere to be seen.
Continuity mistake: In the two early scenes when Shuji is talking with David in the back of the limo, it's clear that they are not driving past the same section of street when the camera angle changes. For example, the buildings change from shot to shot. Also watch when Shuji hands David the bottle of whiskey in the second scene - Shuji's hand moves down the bottle between shots.
Plot hole: In the warehouse shootout at the start of the film a wounded Yakuza brandishing a tommy gun with a drum magazine jumps onto the roof of a car and opens fire. He cuts down a few mafia guys and destroys alot of scenery before running out of ammo. Before he runs out of ammo there is a shot of alot of empty cartridge cases on the floor. The ends have been crimped showing that they are all blanks.