As someone who was a trainer store-side, and probably going to be a trainer DC-side in the near future, part of the problem is how they train trainers. Store-side (at least how I went through it), to become a trainer, after receiving the blessings of your TL, ETL and HR, you take a 45 minute online course a fourth grader could complete and....that's it. No real way to determine if the TM is qualified to teach others in their job function. What they should adopt is a system similar to how the DC trains trainers. After getting all the necessary winks and nods from authority figures, you have to do an essay. I've heard varying things about it, but it's along the lines of why you want to be a trainer/why should you be a trainer/etc. After passing that, then they'll pair you up with a trainer, who you have to psuedo-train in one of your dept's core roles. The trainer will intentional try to do things wrong, so you can give feedback/help correct their actions, as you would in a real training scenario. Only after you pass this, you can then become a trainer.
However, I doubt they'd ever adopt a policy for store-side, as it'd probably be seen as a waste of time and money to go through all of that instead of a simple online course. But if you ask me, training new hires is vital, not only because of the constant stream of new hires in the high turnover world of retail, but because the better trained your new hires are, the more money the company can make in the long run (read: more hours and better pay for y'all) through better GS, better sales, better metrics, better conversion, better unload times, etc.
Sorry for the long-winded response, it's been a long night at the office...