How do I check if a used car is accident free?

What should be considered when buying a second hand car?

Does the number of previous owners matter when buying a used car?

I'm in the market to buy a used Porsche Cayenne 958.1 (2010-2012) but can't decide on the 3.0 Diesel or 3.6 Petrol. The reviews all say get the Diesel, better economy, better torque, cheaper maintenance but those are mostly European reviews. For Malaysia the Diesel has the cheaper road tax and diesel (Euro 5) is cheaper too than Ron 97, but thinking about future resale which is the better option? With diesel losing popularity, Porsche has stopped offering diesel models, is that a concern for our resale market too?