I see that a lot of people are recommending P6, CZ-75B and you are considering an XD.
Well let me tell you because I have all three of them....You can't go wrong with ANY of them.
I am not a big fan of buying used firearms. I mean, you might save $100 or 2, but what's that in a big scheme of things when ammos cost so much these days.
Shooting is like skiing....the intial equipment is NOT the most expensive part if you shoot a lot, so buy a new gun that's not too expensive like XD-9 or CZ75B and take a good care of her. If there is a budget limitation, go for a P6. As much as I like 22LR's, if this is your FIRST and only gun for a while, go ahead with a 9mm.....you can't go wrong with it and it's probably the most versatile. Cheap enough to go plinking and shoot a lot, yet powerful enough for self-defense. If you want to shoot a LOT, then I would just get a second gun, like Sig Mosquito in 22LR.