Biggest common issues are ignition switch recall, transmission failure(mainly in v6 but also can happen in i4)
However some things to consider and possibly check up on...
-Check VIN # /CARFAX
-Check the car body for dents etc...stay in an angle and look at the body lines to see if theres been bodywork done...if you see ripples and not a straight reflection then somethings off
-Check for even gaps at all doors to see if maybe a door has been replaced
-Check for rust both underbody and upper
-Check interior for rips, stains, or water marks if the vehicle has bene flooded previously, look for moisture under the carpets
-Check all electrical stuff from A-Z , Make sure all dash lights turn on, especially CEL, SRS, ABS lights
-If you can hook up an obd2 reader to the car and scan for pending codes or Pending System Tests. This might mean the seller just reset the ecu due to a CEL Code.
-Check for leaks around gaskets
-Check the oil level, is it at the max mark or low? If low it could either means it burns oil or the Original Owner might have not taken good care of it.
-Check the tranny fluid level.
-Tranny fluid should not have a burnt smell, and should be clean and transparent
-Check A/C both Hot and Cold
-Get sum1 to start the car and see what color smoke blows out the exhaust, If blue car is burning oil
-Check for delayed engagement...With the transmission in "P" (Park) start the car. With your foot holding down the brake pedal, shift to the "R" (Reverse) position. Almost immediately the transmission should engage - it feels like the car wants to creep backward. This should happen very smoothly, without a strong jerk or jolt.
Shift to "N" (Neutral), and the transmission should disengage. Now, again holding the brakes, shift to the "D" (Drive) position. Again, the transmission should engage without a delay - you will feel the car wants to creep forward. This also should be without a strong jerk or jolt.
If there is a notable delay (more than 1 seconds) between the moment you shift and the moment the transmission engages, transmission is either too worn or has some problem. During a test-drive the transmission should shift between gears very smoothly without delays, jolts, slipping or shudder.
-Press down on each corner of the car and see if the car keeps on bouncing after you let go, if so it suspension is worn out.
-Test drive the car both in highway speeds and street speeds
-Ask to see if and when timing belt and waterpump were done
-After the test drive park the car but dont turn it off, let it run for 3-5 mins and then move the car and look in the pavement for any leaks.
-If you can and have the means of it, obv get the car raised on a hoist and check things such as balljoints, tierods, shocks/springs, endlinks, bushings etc
