The two sets of golfers walking in the background are inconsistent with the Harts golfing action.
Jennifer's position at the table with Owen and then Fritz keeps changing.
When Jennifer gets out of the golf cart to hit her shot, she's carrying an iron. It also appears as if she's going to hit an approach shot from just off of the fairway on a sloped lie. However, when she hit the actual shot, she's hitting a tee shot from the tee box between the red tee markers with what appears to be a fairway wood. (It could be a driver as club heads were a lot smaller then.)
During the car chase, the license plate of the car chasing Jonathan and Jennifer is 619 UPL. However, when it goes off the cliff, the license plate is 137 AEH.
As Jennifer, Stefanie Powers keeps her fingernails rather short. In the close-up of Jennifer looking at Jonathan's "will," the fingernails of her left hand are seen as much longer.
The golf cart with the bomb planted in it is old and not up to the standards of a self made millionaire.
As the car goes over the cliff, the body that falls on the rocks couldn't have come from the car.
Jonathan comes out of the bathroom, dressed for bed. He is wearing satin white pajamas. They are strangely see-through. When he climbs on the bed, the long shot clearly reveals that he is wearing white briefs underneath. Strange for someone going to sleep with his wife.
When the bad guy says, "omit one Jonathan Hart", his head is down and his face isn't shown. His voice sounds as though it's coming from off camera, as though it was dubbed in.
A squeaking is clearly audible while the Harts are driving in the golf cart, possibly from a camera attached to the front.
Everyone doesn't think that Jonathan is dead; the police know that he isn't.
Jennifer never appears to be a grieving widow to those who don't know that Jonathan is alive.