Dimple on the front shoulders
Thick & big (and therefore generally bad shoulder pads), poor internal stitching and/or extra fabric cause these dimples. While many a times, it is also because our bodies are not perfect and symmetrical; mostly it is due to careless tailoring. Ready-made brands want all bodies of the same neck sizes to wear one standard number of theirs. So this would be pretty common there.
Shirt Cuffs
A good suit has sleeves which are slightly shorter than the shirt sleeves thereby giving a glimpse of your shirt cuffs. ½ a inch is good enough. Slightly more too is fine, but can be decided only when you stretch and move your arms a bit.
Back
Back of the jacket should be clean & fit like glove. Any extra fabric hanging from the sides or wrinkles as seen in the picture is a sign of bad fitting
Collar Gap
A suit is oversized or the collar is cut larger than required if the gap between the shirt collar & the suit collar shows as demonstrated in the picture.
A right sized suit will sit on the shirt collar inseparably.
A right sized suit will sit on the shirt collar inseparably.