Yes it's a good point and i will always do so next time. The caveat is that it was January, -2 degrees and the part was a roof rack. So, encouraged by the year long warranty i waited until the weather was a little better before trialling them.
This is my first experience with receiving a dodgy part, and would now strongly recommend doing an immediate inspection.
As an update, after sending them a letter using a template from the which legal team, Lexus parts direct agreed to replace the faulty part. They collected the faulty one and delivered me a fully functional replacement!
They were also polite and courteous throughout. Well done Lexus parts direct in the end.