You may have heard the ole' plumbers saying that all shi... well, in this case, we'll use ship... runs downhill. As you can see in the pictures, it would be hard for anything to run downhill (including all of the wonderful things that wastewater includes), when the drain pipe is running uphill. Drains also need to be properly supported to the structure.
Although draining at the inspection, it will be a matter of time before these drains plug up. The "water" portion of wastewater may drain out, but the "waste" portion, or solids, will have a harder time draining (if at all), and will eventually block/plug the pipe causing the drain to back up - never a pleasant thing. Drains usually have to have a certain percentage of slope, which varies with jurisdictions, but usually around ¼" per foot of pipe is ideal. Now during an inspection, I'll test the water under normal inspection protocols. I don't bring the latest issue of Sports Illustrated into the master bath and "take a load off" so to speak, to test the toilet/drain. Nor do I test drains by adding hair, small toys, earrings, corn, excessive toilet paper, etc. - all everyday things that may find their way into a drain and lead to problems (especially if you have kids or a spouse with long hair). Again, this is the epitome of poor plumbing workmanship and I can confidently guarantee there will be problems if not corrected. On the bright side, its people that do this kind of work that makes my job worthwhile and another reason a home inspection is always needed.