How legit it this?

The laptop is a bit old maybe about a year or so old. Although it may be brand new, I wouldn't pay for it as a 4th gen CPU and much better graphics card is about $200 more. 😉

I will pay only about $800-$900 for it.
 
Same city as me.

Apple products depreciate slowly compared to everything else.
$1,000 for that is very cheap. Apple sell the same thing refurbished for ~$1,800.

I'm not saying you can never get a bargain. The seller has been registered since 2005 and has nothing but positive ratings.
For anything like that... Pay with paypal / credit card so you can claim if things go south.