Q: buying preowned-can I use serial number or other to get specs?

Are you looking at PowerPC Macs or Intel Macs? This forum is for the PowerPC iMacs, made before 2006.

All the resources I've seen will show the model designation (ex, Mid 2012 MacBook Pro) but not the details about special ordered options.

The donationware MacTracker database:

http:/mactracker.ca

may be the better resource although is does not have a lookup by serial number function. It includes order numbers and, usually, what options/variants a particular order number denotes.

Append the last three characters of its serial number to http://www.everymac.com/ultimate-mac-lookup/?search_keywords= and load the page.

(112325)

Query by serial number

Apple's warrenty database will identify the type of Mac you have.  Your serial number is securely sent.  Provides more information for newer machines.

https://selfsolve.apple.com/agreementWarrantyDynamic.do

This site provides more information.  Best for older machines.  Note, serial number is sent in the clear.

"A serial number is a unique, identifying number or group of numbers and letters assigned to an individual piece of hardware or software. It's used for various things depending on the product / brand but what is your Mac's serial number for and more importantly... what is it hiding and what can it do for you ?"

http://www.appleserialnumberinfo.com/Desktop/index.php

or

This site provides more information, but lacks security too.

"A serial number is a unique, identifying number or group of numbers and letters assigned to an individual piece of hardware or software. It's used for various things depending on the product / brand but what is your Mac's serial number for and more importantly... what is it hiding and what can it do for you ?"

http://www.appleserialnumberinfo.com/Desktop/index.php

http://www.chipmunk.nl/klantenservice/applemodel.html

    ( hint by K Shaffer  )