When the police follow Barrows from the hotel to the store they are tailing him in a light blue Monarch. When they are at the store where Barrows is buying the custom bag, they are shown in a brown Monarch. When Barrows arrives back at the hotel are in the light blue Monarch again.
The B&W photo Kelly presents Bosley with of a group of people on a cruiser deck, clearly shows that Carol Lynley's head (and other people's too) had been pasted on the original person's. Some of those heads are bigger than their original bodies, and clearly stand out from the background.
Obvious use of stunt double: when Kelly (Jaclyn Smith) fights Lin his shop, the double is a much larger woman than Smith (or possibly a male stunt person).
While in the hotel lounge with Bosley, Lisa Gallo orders a Mai Tai but undercover waitress Kris brings her a daiquiri.