Several things to be aware of...
Most have already been mentoned...
1) Keep the gun CLEAN, especially the chamber...
2) Use ONLY "Break Free CLP" as lube...
3) DON'T use laquer coated Wolf ammo...Military brass ammo is best...Even store bought hunting ammo is likely to give you trouble with it's thinner brass and thin bullet jackets...
Ever notice the discoloration (heat treating) on the shoulder of military brass ? There's a reason for it...
5) Use ONLY good USGI mags...No dings, dents, weak springs, or boogered feed lips...
Bad mags are the single most common problem...
If the rifle was used, I'd say check the extractor claw and spring for wear or weakness, but since this is a new gun, they should be fine...
The ejector is usually pretty stiff, so unless it was stuck solid from lodged debris, I wouldn't think it would be a problem...
I can't stress enough, how important it is to keep it clean, use good mags, good military ammo, and to lube the bolt/carrier/upper assy with ONLY "Break Free CLP"...
Follow this advice to the letter, if the gun is mechanically sound, you will never have a problem with it...
GOOD LUCK !!!