Dealerships near me (Edgware, Greater London, GB)

Disgraceful behaviour from the Owner!! I Called and struck a deal over the phone. The Owner of the Company said the Car was now mine!! Asked him for the registration so as to get the Insurance Quote for the Car. Told him I would call back within the hour with my card details so as to place the deposit. He said that was fine!!! I called back 40 minutes later and he said he’s sold the Car to somebody else who had just walked into the office and paid a deposit. Is that the Way to Run an honest Business???? If He can pull a stunt like that then can you trust anything he says about the Cars that he is selling!!!!!!!