Questions to ask before buying a used Rolex?

[DaveS96]

I’ve recently purchased a Rolex Oyster Perpetual Date 15210 2006 model. With an engine turned bezel.
I gather all (including modern produced) models are 34mm.

Secondly what is the history of this particular model as I have heard and read many people refer them as the mix between the air king and the Datejust. I’d love to find a little bit more about it as I’ve had a Datejust before and this seems somewhat different in many ways.

Thanks a lot for your time people. Kind regards Dave