Visible crew/equipment: When Del and Rodney are sitting in the van after the auction you can't see into the back of the van for huge boxes. When they start shouting and screaming the camera angle changes to show the van rocking from a distance, and you can see someone in the back of the van through the back windows banging against the side of it.
Character mistake: During the scene of the dinner, James (Raquel's father) states that he was in the Royal Navy and was "First Officer" (1/O). The Navy does not have this rank since it is a Merchant Navy rank. The rough equivalent of this is Lieutenant in the RN and Albert would've known this but didn't mention anything. It is also extremely unlikely that an officer the RN would still be Lieutenant after doing his full quota of 12 years service.
Continuity mistake: When Del is pretending to be ill, Albert and Raquel say that they called the doctor in the previous evening. However, a few shots earlier we learn that Del was out with Rodney the night before.
Continuity mistake: When Del and Rodney are outside Sotheby's, it is dry. When the van is rocking, it is pouring down.
Chosen answer: An apparent long string of illnesses.