I don't think there were "bad" years for Rangers, except 2013 and up
2002 had 3 engines offered
2.3l DOHC 4cyl Duratec, had heated thermostat and IMRC issues
3.0l Vulcan, reliable but under powered V6, used from 1991 to 2008 in Rangers, so a good "little" engine
4.0l SOHC, had timing chain issues until 2004 model year
Automatic transmissions are tricky in used vehicles, nothing to do with Ford, Chevy or ??.
How they were used and maintained decides "miles to go" before rebuild is needed, same as Clutch for a manual trans, parts DO WEAR OUT
2002 used 5R44E in 2.3l and 3.0l, 5R55E for 4.0l
No real fingers to be pointed at anything specific on these for 2002 model year
4WD Rangers used 4x4 control module in 2002, these were known to fail, I would not say "common", just a known issue.
2002 will have PATS(passive anti-theft system), PATS keys are needed to start the engine
Check fluids, smell fluids.
Make sure Check Engine Light(CEL) comes on with the key, then goes off and stays off after startup
Ask to see the Title, you don't want to pay full fair for "rebuilt" or "salvaged" title
Ford has a very good "Used vehicle check", runs about $150
See if seller will allow you to pay for this test, if not you may want to rethink this one, could just be seller doesn't want the hassle of you taking it in, but he could also be hiding something major.