I looked at MW, Outliers and Tailor Stitch. Outliers and TS currently don't have patterned shirts (stripes, checks, etc), but at least Outliers shows one piece of carelessness they don't match up the patterns on the yoke with the sleeve. (same with front pocket --things should line up).

Since most don't show a picture of the back of the shirt, also can't tell if they have split yoke. Most quality shirts will have split yoke, especially dress shirts, though it's mostly unnecessary.

One other tell of whether someone takes pride in their shirting is not using synthetic buttons.

outlier (similar to MW) does as well -- their reasoning is that the factories in Portugal are the ones which are able to do the highest quality work at their scale