I don't think comparing bicycle frame sizes to shoe sizes is a valid argument. There are roughly 16 standard shoe sizes, not including width. Most shoes aren’t adjustable.

Most adult mountain bike frames, even from Trek, Specialized, etc. come in three-to-four sizes, varying an inch between frames. If X-mart stocks an average-sized frame and there are a few inches of adjustment in the seat post/rails & stem, most folks are going to fit fine.

In any case, I don’t see that calling me names like "Sparky" or suggesting that I'm on drugs, or any of the other standard hide-behind-your-keyboard-and-lob internet bully tactics you’ve employed in this thread is advancing this discussion.

If you had a discussion on this topic with one of your customers in the shop, would you call him names? Would you suggest he's "smoking something?" Use bathroom terms to characterize his drivetrain setup?

Do you think he'd leave the store satisfied that you had given him an articulate and straightforward rundown on the pros and cons of department store bikes?

Do you think he'd come back for more of the same wisdom? Steer his friends away from X-mart and straight over to your bike store?

To get this thread back on track (if it's OK by you): What kinds of low-end Shimano durability/adjustment issues do you see as a bike mechanic? Is it actual material failure, unaided by dirty and/or continuously-used out-of-adjustment gears or other abuse?

I'm sure I don't have anything close to the experience you have in working on bikes, but the 12 or so bikes I've built or ridden over the past 25 years -- using Tourney, 600EX, DuraAce, Centaur, Record -- have never had a part just self-destruct. Some of them have been ridden many thousands of miles.