mac here with some pre-buy tips, this would sound "Goofy" unless I preface it: this helps avoid issues from "whereby I've lately seen - heard - a friend of a friend's experienced it" type info and similar "bad" info that commonly gets passed around by those who are not truly "up" on cars and car assessment...most people who don't work on their cars a lot, or care to know much more than operating and where to take their car to get fixed.
Scenario goes that the "New" used car is obtained (sight unseen; no pre-test of any kind), and very soon it is attempted to start which results in an assessment of FUBAR'ed engine, and potentially a lot of wasted money plus the monies it will take to fix the car

For those who are looking at a car that may not start or run but the owner claims it will, here's some tests to help determine the engine's current viability.
In a nutshell, you (or helper) want to as best possible:
1) Rotate the crank by hand with a breaker bar or wrench at least 3 full turns, testing for collision noises, non-operation, or catches. If any present stop immediatly and do not force things, just walk away right now unless you already expect the belt is bad and engine is toast...because it is if these things happen.
2) If moving freely, try to determine Timing belt backlash is not "Severe" by SLOWLY hand turn backwards, same procedure as above but reversed - it takes almost a "Safecracker's feel" feeling for catches or obstructions, or evidence the tensioners are/aren't still operational as it's common the studs break or bearings seize. If possible (you have time/tools to remove right side timing belt cover, or it's already off), get a visual on the belt's condition as well as the tensioners (down low) if possible.
3) That checking out, next is the cam clocking...best test is #1 spark plug removal to determine if the piston is moving with the cams, and if TDC is achieved at the correct timing positions. A skipped tooth or two on a new TC is a very common mistake for those not "up" on the procedure and will cause the engine to not run correctly, and if off more than 1 tooth can actually damage the valves via collision.
4) Next if above all passes, a thorough inspection of all connectors (looking for corrosion), battery age and connectors, belts and hoses looking for wear also helps indicate the engine's life history and chance of starting up for you. You also definitely want to be SURE the stock clutch fan is in place and spins correctly: not freely unless VERY hot, but as if it's in light oil or something...just a little bit of resistance but spins easily once moving. If notchy or bound up, you have a major cooling issue waiting for you. Same with the radiator, ANY damage or leakage is a huge problem and the cooling system needs a rebuild.
5) If all checks to this point, a compression test is in order (check OSM for proper procedure, which is unlike many other cars BTW) and if that passes, go for the actual 1st time cranking.
This should be the final hurdle, and if it starts and runs well you can move on to other checks such as rust/mold, further needed maintenance, etc.
Now you'll have good baseline on the whole rest of your renovate vs. sell strategy. Avoid this type of scenario: Buddy in Jan bought van, turns out it has a seized motor. The ad/previous owner masked this critical problem by stating in the ad it came with a "bad fuel pump", "starter bad", ignition starter solenoid disconnected, etc. This and the good old "car needs this and that, have the parts but just not installed" are warnings that quite possibly a far larger problem exists, since most likely if all the car needed was the parts installed, the PO would have done it and be using the car.
I know this all may not be your type scenario, but it's the "Principal " here that many people are not honest or carefully leave out critical info hoping you will ignore that missing info, or worse (for you), hope you do not know to ask/look for it.
Glen 11/7/2017
Edit- Just a note to the PO that I cleaned this up (and added a few things I know) as it is very good test info, but was very hard to read and comprehend. Thanks for the good info, Glen.
DCaff