I'm no expert, but if the DA trigger pull is really in the range of 4 1/2 lbs, I would expect that he is selling it because of unreliable ignition.
My impression is that once you get below 7 lbs. DA pull you have to add some custom components to the gun to insure reliable ignition with any primer. I also believe that the first custom part that has to be added is a heavier hammer, which should be pretty easy to spot.
Based on the apperance of the recoil shield and comparing it to my 620 and 610, I suspect the actual round count is probably in excess of 1000 rounds downrange. The impression of the caseheads on the recoil shield looks about the same as my 610 and 620, both of which are currently between 1000 and 2000 rounds downrange. So, it's not a "virgin gun" by any means. However, IMO a S&W with only 1000-2000 rounds on it is still a very low mileage revolver barely past the break-in.
If it times well, doesn't exhibit any push-off, and looks good, I would consider it as a potential bargain. Fact is that if the lockwork hasn't been butchered by some hack job, you can put it back to a near factory condition with 15 to 25 dollars worth of springs and a new strain screw. Unfortunately, making sure the lockwork hasn't been hacked up will require pulling the sideplate and an examination of the sear surfaces under magnification. I would make sure that the seller is willing to submit to this type of examination and if he isn't, just pass on the gun or factor in the cost of a new hammer and trigger into your offer.
BTW, I would NOT leave that trigger as it is now, IMO a single action pull of less than a lbs. is an AD just waiting to happen even if it doesn't push off. Sometimes a trigger can be just too light and IMO any sub 1.5 lbs trigger is too light. In addition a light trigger can be a distinct hazard in the hands of an inexperienced shooter.