Came across a post and saw that newbies have been conned by bad sellers here in CS. http://forums.clubsnap.org/showthread.php?t=226993
Just like to highlight to anyone especially newbie buying used stuffs to be careful.
When you are going to meet the buyer, state your condition that you will be allowed some time to do testing. If any sellers give you excuses that he is rushing or insist no need to test, WALK AWAY!
And when you are testing, ask him/her to SHUT UP and let you test in peace without interruptions. Distraction is a tactic to make you lose your capability and concentration while testing something.