During the car chase between the taxi and the Chevy, the Chevy's left front tire hubcap flies off, and two shots later is back on the tire again.
When Mac uses the forklift to push the barrels and the bad guys into the water, the barrels float on top of the water. Full barrels would either sink completely or be mostly submerged but empty barrels would float on top of the water.
During a car chase where Harper puts the taxi on two wheels like K.I.T.T. in "Knight Rider", you can see several rubber tracks on the parking lot where multiple takes of it had been done but failed and marked the pavement.