That's actually a really good deal if the printer doesn't show any signs of physical abuse. There are videos available that discuss how to put the original machines together, and this information is still helpful in showing you where key problem areas might occur and things you want to check before trying to use a used printer. At the top of the list I would suggest making sure the frame is square, the X gantry (the one the print head rides on) is square to the rest of the frame, and that the eccentric nuts are all adjusted (these are part of the rollers that allow the X, Y, and Z axis to all slide freely).

A couple to get you started out with -- these are for the original version of the Ender 3 but most of the information will still directly apply to the v2 machine. Ender 3 assembly: https://www.youtube.com/watch?v=me8Qrwh907Q Bed leveling: https://www.youtube.com/watch?v=5eqTmb01cBk

The information about bed leveling is critical even if you have an auto bed-leveler. You still want to know how to keep the bed reasonably square to the rest of the frame or the ABL is going to be constantly adjusting itself even for simple prints. One of the key mistakes most people make is to leave the springs (or in your case the silicone spacers) too loose which allows the leveling knobs to freely turn while the machine is printing. This is what causes the common issue of "I have to re-level my bed after every few prints". When done right, you can easily go 6-12 months without ever having to touch the bed leveling. In my case with still using the springs, "done right" means you get all the leveling knobs tightened all the way, then adjust the Z switch to match that position, THEN proceed with leveling the bed. A lot of people just leave the Z switch where it's at and adjust the leveling knobs to that level which results in springs that are very loose.

As far as the printer itself goes... I've had my original model Ender 3 Pro for 4.5 years now, pumped out a lot of prints over the years, and still find it more reliable and giving better print quality than the $2500 printer we have at work which has auto-everything and still somehow fails. Plus I personally really love how easy it is to do upgrades on this printer which allows me to customize it to my own needs. Even my direct-drive print head was 3D printed!