This can only be determined on a case by base basis. For example many brands have a high quality line and a low quality line, and the average consumer might not know how to differentiate them. Such as if one shirt costs 75 and another costs 55, cost alone isn't a complete indicator as sometimes brands will find a way to produce an item for less but sell for more to maximize profits. Or they may open a second manufacturing facility which is less supervised and doesn't adhere to the same quality standards.

Something doesn't need to be literally for life, a thing can be BIFL if it lasts 20 years and the competitor lasts 3-10

This isn't always a perfect indicator, but one option is to look at how much variety the brand has. If a brand makes 25 different types of jackets with differebt styles and materials and these change very frequently and are often steeply discounted at the end of season, it's a shot in the dark if any will be decent. If a brand only sells 3 styles and you only get 2 material choices that can be an indicator that they aren't purchasing materials solely based on cost.

With some brands it seems like their buyers find a good deal on some random fabric, they make a run of it, and then next year they're making a completely different jacket because they got a good price on that.

The best determination is to get into store and examine the product. Look at the stitching. Sometimes you can outright see terrible stitching. If you see stitches like those, it's junk. It might fall apart in a few days.

Price isn't always a good comparison, as some junk sells itself on reputation, and they charge 400 for something that's only worth 100