When you pump a hydraulic floor jack, the lever does not go directly up. It swings around its pivot point.
This motion-on-a-circle action means that the point being lifted will move sideways, relative to the original place where you planted the wheels of the hydraulic floor jack.
The movement of the wheels in turn means that the hydraulic floor jack must be positioned on a smooth floor, and that all wheels must be well lubricated. Failure to pay attention to this (wheels stuck, for example) means you'd be lifting your vehicle sideways, possibly damaging the beam you're lifting, or the vehicle could fall (potentially leading to a nasty accident).
(a) Is my understanding of the use a hydraulic floor jacks accurate? (b) Is that (one of) the difference(s) between a $50 jack and $500 one?
Anecdote: The jockey wheels on a bicycle's derailleurs are almost always built without ball bearings. One has to go to the very top of the range of bicycle derailleurs to find components using ball bearings.
(c) Is this the case here as well, and buying a reliable, safe hydraulic floor jack requires wheels with ball bearings? (d) What else should one be looking for when shopping for a hydraulic floor jack? Lifting a ~1500-2000 kg vehicle (the majority of sedans, hatchbacks, and SUVs) — or ~3000-4000 lb — should be amply supported on even the weakest two-ton hydraulic floor jacks.
The crux of the question is part (c) above. Parts (a), (b), and (d) are for "extra credit". They educate the pupils rather than just have them memorize a quick knowledge bit, and they confirm that the teacher is knowledgeable and will not just provide a one-word answer.