Reliable places to purchase MacBook Pro 15" 2012 non-Retina i7 and Fair Price

[rocknpop]

I'm' looking to buy a MacBook Pro Mid 2012 i7 quad-core and I have two questions:
1) What are the most reliable places to purchase a computer this old and in the best condition available, without worrying that it's stolen, has something wrong with the motherboard, etc?
2) What is a fair price for a used but in great condition (standard 8GB or RAM and the basic HD)?

 

[chuxdaddy]

I just bought a Macbook Pro 15" (retina) i7 from
www.macofalltrades.com

I have purchased 3 macs from this reliable company with a 90 warranty.

 

[rocknpop]

I just bought a Macbook Pro 15" (retina) i7 from
www.macofalltrades.com

I have purchased 3 macs from this reliable company with a 90 warranty.

I just checked, but they don't have the configuration I'm looking for. Any other similar websites?