Watch out for Lacquer or other clear coats on copper fixtures.... I have several Kichler copper and brass path lights out in the field that I installed about 7 or 8 years ago... They came from the factory with a clear coat on them and it has not stood up very well. Now the fixtures look awful... they are all blotchy... shiny where the clear coat stuck and patina where it flaked off over time. (sort of like the Mercury mag wheels on the wife's car)
A clear powder coat finish might be a lot better then lacquer, but if we are talking about demo fixtures, you have to think that they would take a bit of a beating as they get moved around etc. Stuck in the ground and left alone... who knows, they might stay shiny for 10 years as claimed.