As far as I remember, with a VIN number you can get a report with the car’s history. I am not sure how much this info helps when buying, because anyway it will be incomplete.

It helps of course. I would even say it is a must if you are buying a used car from someone. Sellers can be different, and there are those past owners who are ready to roll back mileage, hide part replacements after accidents, just to sell you the car more expensive than it really is worth. For a VIN report you can use services like FAXVIN to order a report with full official info. That is not enough of course, because that info is only from official sources, but it is still very important. The rest you check with a specialist, like a mechanic.