If you are looking for a new coat than we really suggest you to read some of our guides first. However, if you are hurry than you can just remember some basic things:
Investigate the collar, does it look like it will break its shape?
Check the buttons with an easy tug, is it still there? Loosing buttons with a whiff of air is a sign of bad quality. You can say the same to a vendor though.
Trust the well-known brands such as Columbia, North Face, etc. Their coats may be cost more, but they will serve you for a long time. You can use such coats for ages, way better than buying a new one each year.
Shopping for a good coat is not easy, especially when there's so many varieties. Avoid speedy decisions, read available information, learn all tips, and choose a right coat for your needs. And bad weather will not be able to keep you indoors.