Does primer inhibit rust?

I want to paint my car flat black, as in black primer, no clear coat. Someone told me that this would make my car rust out prematurely. Is this true? How are so many show cars painted flat black if it makes them rust? Any knowledge would be greatly appreciated.

primer is used to help the paint stick , the metal will still rust under primer unless you sealed the metal before priming , if you want a flat black car get some flat black paint ,

where can one buy the metal sealer? Are there any brand names or a common name for it?

just go to an auto paint store , not really a best brand to buy , just talk to them there and see what they have to offer