For both type, check things like functions to see if all are workable, condition of lens, check if flash working, batteries to see if any damage or able to charge. If digital, take pics and zoom it fully on the LCD to see any spots or markings. Film wise check if film motor is working and take some shots to see if shutters working fine.
U can also try at different shutter speeds and even bulb mode.
Depends on yr budget and needs. For me it's only an SLR and nothing else cos i love the feel and superior control of SLR. Go film (like myself) if u're low on budget and very particular about image quality. DSLRs save a lot on film and processing costs and can view results immediately on the LCD. Film ones can really train yr confidence for each shot as of cos, there're no LCDs at all.
If I am buying a camera in CLUBSNAP B&S, I usually check the past posts of the guy selling it. You can tell if that guy is pro, amateur, etc. I usually try to buy stuff from hobbyist who seldom use their camera. I never buy from pro as my take is that they use their cameras MUCH more often.