The active ingredient in marijuana is delta-9-tetrahydrocannabinol, not "tetrahedral chloride" as identified in the film, other than the comparison to pot, the character's description of absinthe is otherwise correct
When Cassie first looks at the blurry picture of Richard from the ATM there is a Range Rover in the background (to the left) but when we see the picture later, after it has been cleaned up, the Range Rover is gone.
This happens in the two times (the same scene twice along the movie) that we see the finding of the corpse (that it is revealed after she is alive; not Olivia). The first time the police woman takes the arm of the body and look at her partner on the upper side and is him who reveal she (the corpse; not Olivia) is alive because she moves her fingers. The second time the police woman takes her pulse and looking and her, the woman wrapped in plastic, says that she is alive; and it is presumed that it is the same scene.
It is said that there are no fingerprints from Justin or Richard, but they are shown carrying Oliva's dead body wrapped in plastic to the car and neither of them have gloves on, thus there should have been fingerprints from Richard and Justin found on the plastic that the dead body was wrapped in.
The goof item below may give away important plot points.
In the opening scene, an aerial camera shot zooms into the house on the sea cliffs. Initially, you can tell that the cliffs are some distance from the edge of the house. Later the small and busted up decking is immediately overhanging the cliffs, and Richard falls straight down to the rocks below. The decking would have to be huge to allow him to fall to the sea.