Nice. A couple points that were brought up that I didn't think of:
-collar gaping (although I think this is more of a symptom of a low arm hole, another cheap suit indicator. Although even budget brands have been raising their armholes recently)
Seems like lapel roll is a common one.
Buttons: Can't say I completely agree with buttons, I pulled out my Isaia and Kiton suit and they both have pretty run-of-the mill plastic black buttons. Although I suppose if one were to have really nice horn buttons this would be a good indicator...but once again, I can't differentiate fake palstic horn from real horn unless it's up close (that being said I don't really have a discerning eye for buttons)
Keep it coming guys!
It's pretty easy to spot the differences between a cheap suit and a decent suit. The decent, entry-level suit, in my book, is something with at least some canvassing, a lighter fusible and generally doesn't go for less than 600-700 bucks (transaction price, not "msrp"). The giveaways of the cheap suit are the over-constructed, no-slope square shoulders, stiff chest drape (over-padded chest) and limp lapel roll. Collar gap issues, IMHO, stem from poor shoulder fit coupled with the stiff chest pad. I have an older MTM (full canvas) that has fairly low armhole and I have a pretty wide range of arm movement without any collar gaping because the shoulder slope and size are correct and the chest of the suit can move and deform naturally. On the flip-side, I have a truly horrid (but well altered) suit (from an SF hated retailer whose name I will not mention) that, despite having quite high armholes and looking pretty well fitted in robo-pose, will gap once I move my arms around even somewhat (in my defense, this suit was an emergency, lost luggage purchase in a place with no other options in my size range - I now use the suit as my air travel condom).
When you move from the decent to "mid-range" (1,200 and up) suit, it's trickier to spot the differences, but again it usually revolves around the shoulder fit and chest drape (an especially noticeable difference between say a 700 dollar RTW suit and a 1,500 dollar MTM suit). Some things like stitching and little details on close inspection are pretty obviously different and looking under the collar at the stitching usually highlights some pretty stark quality differences between the 700 dollar and 1,200+ price points.
IMHO, it becomes very difficult to spot the differences between, say, a 1,500 dollar "mid-range" MTM suit and the 4,000+ dollar range MTM and bespoke suits. I have a few bespoke and high-end MTM suits that, using visual observation only, I can't easily distinguish between (qualitatively) those suits and my "daily" mid-range stuff. Wearing them, however, is a whole different deal; at the 1,500 dollar level you are always aware that you are in a suit whereas my top-shelf stuff feels like I am wearing comfy pajamas (while looking great all day long).