I would say that yes, you can get money back if you are sold a dodgy car, but it can be a bit of a pain. In my case I had to go as far as court action, which was a hassle, but actually quite easy and cheap. I vaguely posted about it at the time, but now it is a matter of public record and I can post about it without worrying about the court case, here's the full story (probably mainly for my therepeutic benefit rather than anyone else!)
So, I had a car I bought from Derby Car Centre, a mid sized second hand car dealer in Derby, UK, who for obvious reasons I would not recommend anyone buys a car from (see below).
After less than a month of driving, it had some problems, and it turned out that these were due to a deliberately concealed engine fault - the engine management fault warning light had been taped over inside the dashboard to conceal this(!).
The worst thing is that when I test drove it before purchase, the light was lit, and I noticed it, after which they said they'd see if they could fix it. Rang me up the next day saying it was just something (some car thing, I dunno), and was all fixed, and I test drove and the light wasn't lit.
So I had the fact that this light had been showing, and the fact a repair had been done which they'd put in writing on the invoice. So essentially I had a ton of evidence showing that the car had been deliberately tampered with while in their care.
Despite all that, when I discovered it, they absolutely refused to take back the car, and was left carless for a good few months. In the end, I took them to court, at which point after much delaying, they put in a supposed witness statement, saying that they were coming to court to defend themselves. Then they didn't turn up to the court hearing, so not surprisingly it went against them. A week after that, lovely high court bailiffs popped over to see them with a debit card machine and persuaded them to part with all my costs (insurance, tax, cost of the car) plus bailiffs fees, court fees, which cost them something close to 3 grand, for a car that originaly cost £1800!
Funniest thing was that once they'd paid up, while I was waiting for the money to clear into my account, they hassled me loads about getting hold of the car. Which I notice almost 4 months later is still on their forecourt for sale at a suspiciously low price!
(http://www.ebay.co.uk/itm/2002-NISSAN-ALMERA-1-5-S-/190586122296?pt=Automobiles_UK&hash=item2c5fd17038 in case anyone is interested!)
It probably helps that my wife is a lecturer in law, so I wasn't desperately scared of the legal stuff - funny thing about that is that I mentioned this, and that I was completely aware of the law on rescission due to fraudulent misrepresentation etc. when I went it to ask for a refund the first time; not only were they very threatening and also generally ill informed and wrong about their rights, but one of them said to me "If your wife is a lawyer, then I'm Father Christmas", if I ever meet him again I guess I'll take the santa hat (and say thanks for the early christmas present of two and a half grand!)