There are a number of things a shopper should know about a car before they ever start the engine, some of which they should do before they even visit the lot or place a bid on ebay!

#1 Get the serial number of the vehicle and call a dealer selling that make.  Ask for the service department then ask them for a WARRANTY CLAIMS HISTORY on the vehicle.  All manufacturers now have internet links to their dealers and this record can be checked online in seconds.  A vehicle that has had a couple of minor recalls or a little warranty claim or two is not a problem.  A vehicle that has had a number of claims ESPECIALLY multiple claims for the same electrical or drivability problem is an invitation to trouble and one to avoid.  It will also tell you the warranty status and if the warranty has been cancelled by the manufacturer for such things as flood damage which may not show on any other source. 

#2  Ask for paint depth gauge readings on the vehicle if you care at all about it being rebuilt from an accident.  Yes, there are online sources that will tell you of accident history - but they are limited to pretty much only those items found in public records.  A remarkable number of accidents are never reported to law enforcement or insurance companies by drivers who fear the worst because they were driving under the influence, have no insurance and other personal reasons.  They typically have the repairs done as cheaply as possible and hope no one is the wiser.  These paint depth gauges cost about $850 but most major dealerships (at least in our market) use them to evaluate a customer's trade in since no legitimate dealer wants the legal liability of getting "stuck" selling a rebuilt wreck.  Interestingly, even though they use them on trades, a fair number of dealerships will deny having one and some will even claim they don't know what a paint depth gauge is to prevent the customer from checking their inventory.  Avoid these sellers as well since they can't possibly tell you the truth about the vehicle.  If you insist on going ahead in spite of the lack of information, at least check all the major body panels for paper strips with the serial number placed there by the factory on many makes from Honda and Acura to Toyota, Lexus and more.      

#3 If you are inspecting the vehicle in person, BEFORE you ever start the engine pull the oil dipstick.  If the oil isn't freshly changed it tells you a lot about the seller.  An oil change is THE cheapest form of maintenance and if they haven't even done that you can bet they don't know how soon the brake rotors and/or pads will need replacing, if there are any metal shavings floating around in the transmission fluid and so on.  Avoid the vehicle AND the seller.  Also check the radiator fluid.  It should be bright and clean.  If it has so much as a single drop of oil or is dark and discolored, there's a good chance the head gasket has a tiny leak that will only grow bigger in the coming months and miles.  Just fixing the gasket may cost $800 while on most "zero tolerance" engines it will mean a new head or engine.  Why?  Because there will be corrosion at the point of the leak and "zero tolerance" means just that - there's no room to grind out the bad spot and not have the valves smash into the pistons.   Transmission fluid?  It should be clean and not smell "burnt" though that may be difficult for a novice to discern.

#4 Flood inspection:  Open the trunk and check the spare tire well first.  Everything should be bright and clean, dusty at worst.  If the tire well has silt in it - run!  If the tire changing tools have tiny pits all over them, they've been wet.  Pull off some of the trunk lining (most cars have access panels to change light bulbs and such) and look for silt.  Check the engine compartment.  Steam cleaning can remove dirt but it won't remove corrosion caused by submersion.  Run the heater on full blast or if it's summer, sniff deeply as soon as you open the door.  If it smells strongly like mildew, there's a problem.  It has been said there's a half a million "flood cars" from hurrican Katrina alone, don't YOU buy one!  

#5 KNOW WHAT "CERTIFIED" MEANS at this particular dealership.  Now that customers know the value of a factory certified warranty on a used car, many "aftermarket" companies are selling banners, window stickers and other advertising items to imitate a factory certified program.  The truth is, many are simply advertising gimicks designed to get you in the door and ultimately sell you something else of equally questionable value.  Factory certified programs all have guides the dealer must follow and require extensive checklists of reconditioning to qualify the vehicle for a warranty.  Expensive things like brake rotors, pads and tires must meet factory standards while maintenance services such as oil and filter, transmission fluid and more have to be performed.  The "aftermarket" certified programs rarely require so much as an oil change let alone other services.  Factory certified programs normally provide "bumper to bumper" warranty for a minimum of 12 months/12,000 miles with longer terms on powertrain and most important, are ZERO DEDUCTIBLE.  The "aftermarket" certified programs are normally for a month or two, maybe three and cover only limited items.  These programs often require the customer to return to the selling dealer for repairs while factory programs are good nationwide.  Also, they are frequently 50/50 meaning the customer REALLY pays the whole bill after it's been inflated.  These dealers hope to sell you something called a service contract or extended warranty to fill in the many gaps in their "aftermarket" certified program.  Generally speaking, ONLY a selling dealer of a particular make can certify their particular brand with a factory warranty.  A Chevrolet dealer for example cannot certify a Honda with a factory warranty and vice-versa.