In the biker bar scene, it's pouring rain when Fletch goes in. It's dry when they come out. Then the roads are wet again when they go riding to the train. Then, after they jump through the boxcar, it's dry again.
When Fletch visits Calculus, Calculus is wearing a pair of brown boots, but after Fletch sits on the water bed and after the comment about the Reverend, Calculus gets up to change the TV channel. He's not wearing his boots anymore.
When Fletch is being wheeled into the morgue by Calculus, Ben Dover removes Fletch's wristwatch and puts it on his right wrist. When Ben sits down at his desk, the watch is on his left wrist.
Fletch attends two different tapings of the Jimmy Lee Farnsworth television show, but the announcer introduces both of them as the "4,323rd edition" of the show.
When Fletch first sits on the water bed, the guitar falls from the wall. In the next shot the guitar hangs on the wall, although nobody put it back there.
Ben Dover claims to have a 78 XL, which is a Sportster. Unless he customized it, the tank and seat are wrong for an XL, We cannot see the engine, so it's impossible to be sure.
When Fletch leans on the railing outside his 'new' house and the railing collapses, you can see that the top rail has been cleanly and evenly cut vertically so it will break away easily.
When Fletch pulls over at Becky's office he uses a parking meter to stop. You can clearly see that the parking meter is already cut to break away easier, and does so when he hits it.
During the opening scene, as the camera is zooming in on the men sitting at the table, Richard Belzer is facing the camera, and its movement causes him to look directly at it. He then immediately looks away, realizing his mistake. He also does it again very briefly as the camera is about to pass by his shoulder, again looking away almost immediately.
During the first scene in the newsroom, as Irwin 'Fletch' Fletcher and Frank Walker walk through the office, we see a map of Long Island, New York on the wall in the background. The newsroom is supposed to be in Los Angeles, California. (The scene was filmed at Newsday's Melville, Long Island office.)
Fletch would never fit into Becky's blazer. Even if Chevy Chase weren't 6'4", a blazer sized for a woman would not fit a full-grown man.
[20:17]The policeman who throws Fletch in jail is the same one guarding Amanda Ray Ross' house when Fletch comes back disguised as an exterminator, yet the cop doesn't recognize him.
Since Fletch's property is where the toxic waste is being dumped, why would Ham Johnson want it?? The property, not the toxic waste.
In a callback to the first movie, Fletch uses the Underhills' credit card to break into Amanda's office. However, in the first movie Fletch only made fraudulent charges on their account at the country club and to pay for a trip to Brazil, he was never in possession of the physical card.