More information about a used Rolex Datejust (image included)

[supermanrox]

Hi,

I'm looking to purchase a used Rolex. I'm going in person to look at it later today, but wanted to some more background information about the model as I'm fairly new to Rolexes. It seems like the reference number for this model is 116243.

My questions are:
Is this a factory model, or is it aftermarket/modified?
I'm looking at it later today. What should I look at and inspect?
What is a reasonable price range for this model (both with and without box/papers).

Additionally, any general information about this model would be very helpful.