Yes, they may be faulty, yes it's too expensive to have a mechanic check them, but hey, if they sell quick and I can rip people off for a few quid... why not? Money money.
Honestly, you're asking this question in a forum? You sound like a proper piece of work. Go out, take some of people's hard earned with your unchecked faulty cars. Yes, you can do it, very easily. Cheap cars sell, if they're faulty or not, so if you can lie and hide it you'll make some money. Remember though, the world will catch up to you.
To all the old, proper, members on here ---- don't entertain these threads in future. We're educating the kind of people we don't need in this game.