That post is perfect. How did you identify the Porter so specifically? I can't see the model # even when the image is enlarged... do you really know each model that well from sight?
Porter Cable doesn't have very many kits (nor do most, really), and those kits were somewhat specific to certain models. The difference in the lettering for the model # is what came in the kits. That Craigslist link shows the newer version of that Porter Cable kit (they redesigned the case from side-by-side to the upper-lower look you see there).
MAKE SURE that the D-handle is included. The 3-piece kit from PC usually refers to the plunge base, the "mushroom ears" handle fixed base, and the motor. That D-handle is a separate-purchase accessory unless that's a REALLY old Porter Cable kit (which it doesn't look like).
Porter Cable offered the 3-BASE kit (notice the difference in how it's worded) quite a while ago, and dropped it for the 2-base (3 PIECE) kit for cost reasons, I'm guessing. They also still sell the D-handle accessory. From all the pics on that Craigslist link, the D-handle looks to be a SEPARATE piece, but he seems to be wanting to sell the whole shebang.
That kit, with just the blow-molded case contents, sold for ~$200, and that D-handle attachment is a $40-60 ADDED accessory purchase on top of that. Those are normal prices you could have found that for from Home Depot, so he's lopping off about $100. The only reason I can think of that someone hasn't jumped on that thus far is that he's not throwing in the D-handle, or they're expecting to talk him down to $100 or less (or whatever the ridiculous offers are given to him).
$125 isn't an unreasonable offer to shoot out there, but going lower IMO will simply get you no response. $150 is a price for that thing that I'd be jumping all over - go donate some platelets for a few bucks or something, but snatch that up!