Okay, if he wants to purchase this particular rifle then to me, he should be able to have the sales guru slip any assortment of mags into it to see if they will indeed fit properly prior to making the purchase.
Lots of guys buy gun show parts and pieces then when they don't fit right they bark up a tree at anyone that will listen to them. Oly has one of the best warranties in the industry, they can get the thing working. Lots of companies try to do the best job they can to fill orders, hell the AR industry is going full steam ahead and has been that way for several years now. It seems no one can stay ahead of the game. So wouldn't you think that filling orders is more important than test firing each and every AR that is produced. Geeze guys a mag don't work, this ain't right and that is wrong.
Guy's like Dan Carey and Mike Milli have the time to hand pick each and every part when building a gun. Still, something, somewhere is not going to be right every single time. For every 1000 AR's that are built every day, you are bound to have a few problems.
Thermold mags have had issues in several uppers and lowers. How do I know this, well after coming from a nearly 700 man sheriffs dept, we had our share of junk mags. I handled and tested lots of AR's and truck loads of mags with thousands of rounds of ammo. My money is on GI issue mags and the newer Magpul products, those are all I use and I seldom ever have problems with my AR's malfunctioning.
Bushmaster sold tons of AR's and many came with garbage mags, never heard a good word about Bushmaster for a long time. I'm still not sure if they have a fix. Armalite AR10's had the worst mags in the industry but now they figured out what was causing the problem, they changed their mag design and now they work great...well better anyway.