In theory, shopping a chain store is fine. Or it would be fine, if you weren't shopping for something that someone else spent years designing and refining. It would be fine, too, if you weren't dressing yourself to appear again and again in the photos, videos, and memories of your loved ones for the next, say, five decades. Or if you weren't investing in something with, oh, just a few centuries of historic and symbolic meaning behind it.
So, when you say you're considering buying or renting formal wear from one of those big chain stores,
we say that maybe you should reconsider.