According to Astra Zeneca (Oxford vaccin) their vaccin has efficiency of 70% (but such should be tested by independent labs)
My car dealer also promised with my previous car it had efficiency of 20km/liter but I have never seen that even when my car was brand new
Your car dealer is not going through the European Medical Agency or the British one or any other country that has approved it. Astra Zenecas vaccines might be the best thing earth has right now, its cheap, good and easy to store.
BionTech and Moderna are to expensive for the developing countries and hard to handle.