Could the watch have been measured in an inexpert manner and in fact is a typical 34mm model?
33.3 seems a bit small for the models being sold by Omega when the 501 automatic movement was first introduced, especially for the models featuring the newly introduced full rotor automatic movements.
I wouldn't mind if the watch measured 33.3mm and would be happy to wear it whether 33.3mm or 34mm. All my watches don't have to be as big as the wheels on the average city bus.
The asking price is excessive. $450 to $600 would seem to be in the Ebay price ranges.