When Banacek first starts to give his solution to the case Gretel's hair changes from shot to shot.
When Carly is taking the ransom money to be delivered she tells Jay to go 8,6 miles past the Interstate 12 cutoff. I-12. Interstate-12 is in Louisiana, not the Boston area.
The helicopter used is a Hughes/MD 500. These have a 5-bladed main rotor. The sound heard is that of a helicopter with a 2-bladed main rotor such as a Bell 206 JetRanger.
When Banacek and Carlie talk at the market, the voice overdubs are sometimes out of sync.
When Banacek climbs a ladder to talk with the sculptor, the boom mike can be seen popping up from the bottom of the screen.