Just a comment about tone; I wouldn't describe celtic (i.e. flat, uncarved top and back) style mandolins as having a 'bark'. Most of them have a softer, ringing tone with plenty of sustain (for a mandolin). It's the carved top F and A style mandolins that tend to have that dry, woody 'bark' that is so prized by bluegrass players when playing the characteristic off-beat 'chop'.
Having said that, there are some categories of what to look for in a mandolin.
Tone; does the mandolin sound 'right' for the intended music?
Volume; is it loud enough to be heard in the proposed setting?
Playability; Is it easy to play, and does it play in tune? Do the strings stay in tune?
Appearance; down to personal preference, but the fit and finish should be acceptable.
Most of these factors can be improved after purchase by changing the setup(except volume; it's hard to make a quiet mandolin louder, unless you amplify it). If just starting out, I would say the most important is playability; a high action and poor neck will build bad habits very quickly.
Tim