In the opening sequence, the note left on the car steering wheel is not what the character wrote. The first line (the 'To' line) should have been "Edna -' - the note attached to the steering wheel is missing the dash (the printing on the attached note is also much neater and straighter than the character's handwriting).
The "suicide note" that Jack Culross clips to the car's steering wheel is
not in the same handwriting as seen when the deputy sheriff looks at it.
Perry and David use a thermocouple to determine the exact date that specific portions of a painting were executed. A thermocouple cannot date a painting that precisely.
When the police stop Miller in his sister's car, it is supposed to be at night. But neither car has its headlights on, so the scene must have been shot during the daytime with a filter.
The door on Clint Miller's jail cell clearly sounds like a wooden prop when it is opened and closed.
When the policeman pulls over Miller in his sister's car, the light on the roof of the police car isn't flashing.
After Edna bites her husband's hand and knocks Jack out by pushing his head against the car one evening in the gallery's dark parking lot, she visits Mason in his office. The shadow of a crew member's head shows prominently on the edge of Mason's desk during their conversation. As Mason begins to rise from his desk, the shadow quickly moves off the desk.
Perry Mason's plane from LA to Dallas is flying over the ocean.
In the epilogue, David Gideon asks Perry if the buyers of Culross' paintings were defrauded. Perry responds that they weren't, because they were genuine. Then Edna Culross mentions that her late husband's paintings are now worth more now that he is gone -- yet when Durrant sold the works, it was assumed Culross was already dead -- therefore the art pieces should not have increased in value from what Durrant sold them for...