no oil pressure

I think ive checked all iam going to check. When I get it home I will pull the pan and check the oil pump then I think iam going to pack it up and send it back and let the builder fix whatever.
Remember this all happened when I started the motor at a store where I had just driven it. It had 40 lb. oil pressure when I turned off. It makes me think something broke on start up?????
The motor only had 270 miles on it.