Is he also using factory ammunition, and not reloads? Although the factory magazines are probably fine, it would be a good idea for him to get ahold of some higher quality magazines. I know that i bought a new Colt brand 7rd mag for my springfield, and when using it, my gun had the first failures it has ever experienced in its lifetime. I had a couple failure to feeds and a couple of stovepipes.
After using the magazine a few more times and giving it a good cleaning, it has worled fine, although i still dont trust it and use it strictly for target duty.
Some all around good magazines that are universally recommended
Tripp research Cobra mags
Wilson Combat magazines
Chip Mccormick Power mags
Metalform magazines
I have 2 factory Springfield 7rd, a kimber stainless 8rd, a Wilson combat extended tube 7rd, and a Colt brand mag (checkmate produced, i believe)
I use and trust the Springfield magazines the most. It is believed that a 7rd magazine will be more reliable/durable than an 8 or 10rd, also there are many different types of followers and fwed lips, and combinations of the two.
Before he sends it back to Sig, have him try a different quality magazine. If this doesnt work, he could always try and tune the extractor, with help from the internet. They are not expensive, nor hard to get to or replace