o First of all, are there any spare ones ? If yes, this is a good sign of quality. Actually it means that the designer expects the garment to last long with minor repairs and wants you to make it right.
o Check the button holes: make sure there's no loose threads and they are properly done meaning they're straight, made at the right size for the button
o The buttons: are they sewn on well? Do they look good? Plastic ones could easily break so make sure they are resistant.
Then, you can test them out and see if it's well done (not too tight or too loose).
To finish, one of the best ways to judge the quality is to try the garment or the footwear on. Feeling the fabric may get you to realize it!
If you have any tips to share, do not hesitate guys! I would be more than happy to add them on,