Dishonest seller/complained and tried to get money back.

On the 19th October, I purchased aNissan Almera from Imran Khan in Oldham, that was advertised on gumtree. At first he seemed a very honest man, and told me that the car makes a noise when driving it, but not to worry, as the car had not been used for 2 years, and the noise from the gear box, would go after I drove it for a while. I went to the post office with him to pay the tax on the vechicle, as it was being sold withe no tax. I also accompanied him to get the window fixed at a garage owned by some of his friends, as when he started the car to show it me he accidently left the key inside with the engine running, and had to break a side window to get in to get the entry. I was a bit worried about the noise from the engine but, he assured me that would go after I ran it for a while. He seemed an honest man, so I trusted him. Since then I have paid for the spare alloy wheel to be put back on, and a service. The noise from the engine continued, so I rang him up and told him I was not happy with the vechicle. He said I should give it a chance for the noise to go, because it had been stood for a while, so I reluctently agreed to give it another week. In the mean time I had it checked out by 3 seperate garages, and they all said it needed a new gear box, which would cost me over £300 pounds, one garage said it should not have passed its MOT, it had 12 months, because of corrosion along the front T - bar panel. He said I should take it back or ask for my money back. I rang Imran, and he said he would get his friends at the garage to fix it in Oldham and pay for it himself. But his friends were the one who passed the MOT, for him and I was worried they would do a cheap job on it. I thought about it, and asked Imran to at least give me half the money that I had paid for the car, since with all the work that it needed, it wasn't worth the money I paid for it, to put the money towards a new gear box. I paid £450 for it, but also bought the tax disk. I have contacted him several times, with absolutely no reply, so went to see him at his place of work at Smithfield market in Manchester with my cousin and my brother to sort it out. He started shouting at us all and making excuses, and then just walked off. When we said we were phoning the police, he quickly got into his car and drove off. Since then I have contacted him several times to sort it out with no reply. In the end I texted him to say I wanted my money back for the car, as it wasn't worth what I had paid for it, with all its problems. Since that time, a few days ago, I have heard absolutely nothing from him. I feel that he just wanted to get rid of the car on some unsuspecting buyer. I have been more than fair with him giving him chance after chance to get back to me and resolve the issue, even prepared to bear some of the cost myself, but abslutely no reply from him. Can you tell me what your policy is for rouge sellers, advertising on your website, and can this issue be resolved by yourselves buy contacting the seller? Hope to hear from you soon. Thank you.