It's known in the motor trade to offload problem vehicles in auctions. Garages/retailers etc often sell private to do the same, if they're a small outfit or one man band. Search online for his phone number to see what else he's selling, or sold in the past. The relevant authorities would want to know about someone selling private whilst in business. Also if it's unsafe (fire hazard and brakes dangerous) the relevant authorities would be interested. Normally these types of people know how to navigate the rules and do so to cover tracks. Don't use Halfords. Find a proper local garage to check it over for you. Fighting the seller will always be difficult, more so if private. Hopefully it's quick fixes. Unfortunately you have made some mistakes. You should ask to see the log book before buying, and sellers ID. If you don't know about cars/mechanics then you should have taken someone who does, or paid for an inspection like the AA. You could go and see the person on the log book if you have contact details but if he said he was selling for a friend or it's part ex then alarms bells should have sounded.