If you offer what you are going give them they don't turn up , simple . People are inherently greedy , so high offer gets them on site then appraise the car in question and offer whats its worth , All used cars are different and I've only ever seen two cars in decades that were what I'd call looked after .
Owners know their car is a pile of shite and they tell lies to sell it , They just need to be told face to face . High offer gets the face to face meeting .
They wont block you , Just use an email thats made up