Authorized to work on apple products,?

You would need to ask Apple. I am quite sure they require a certification of some sort so that you can repair a machine and keep the warranty valid. If you try repairing the machine without this, Apple will void the warranty. The exact certification / license you require needs to be reviewed / OK with Apple.

I do not see any Apple repair stores around me - lots of Windows repair shops.

The answer is yes.  It means an actual certification by Apple.

@David Johnson
You're not going to repair a motherboard as that is time consuming and prone to error, especially if they're multi-layer and surface mount part.  It's not going to be worth the time and effort for the amount of repair.  If it were your own equipment and you wanted to spend time on a motherboard repair (for fun or education), then have at it.

some people do it for a living (and a good living) repairing Apple motherboards. Getting donor boards (for parts)  and board views and schematics is problematic (not insurmountable)  Rossmann Repair Group does a board repair for a flat rate of $450USD (operates in Manhattan which is pricy by itself, cheaper elsewhere, no fix no fee approach ) and has a steady supply of customers.. I wouldn't do one-offs If you already do SMC repair you already have a micro-pencil, hot air station, microscope,  all you need is black market schematics and board views

A few years ago Apple shut down their Authorized Service Provider + reseller program + brought all this back in house.

Maybe they've changed this + if you were an Apple Authorized Service Provider, you'd know it... because you'd have to likely take some expensive course + pay some expensive yearly fee to participate.

If you open a machine case + aren't an Apple Authorized Service Provider, you void your client's warranty.

Opening a machine case does not void a warranty.  Please don't promote that lie.

Even if your written warranty is voided, you may be protected by an implied warranty

Under federal law, the merchant must prove that a defect was caused by the alteration in order to void a written warranty.

http://consumer.findlaw.com/consumer-transactions/what-will-void-a-warranty-.html

Opening and closing a case may not void the warranty, but fixing a board (evidence of a hardware repair) by an unauthorized person likely will void the warranty.

Replacing parts will not void a warranty.  They need to prove that a repair caused damage.  If you replaced the screen and it worked for a few months before the battery fails, it will not void a the warranty on the battery.  They have to prove that the screen affected the battery.

Replacing parts will not void a warranty   <-- Removing a circuit board part and soldering a new one in will not void Apple's warranty?  Intriguing.

thanks team