The owner does not allow negative comments about her products on the Facebook group. The owner does not allow comments about other clothing or other websites (Instagram, Pinterest) on the Facebook group. The owner blocks and removes people from the Facebook group for violating these terms, so if a user, say, posts a photo of themselves in a PUG shirt but a different pair of pants, the post will be taken down and in all likelihood the user will be banned.
So there aren't a lot of places I can say that the clothing is just not well made. The fabric is cheap--thin, threadbare, stretches out. The construction is not good--despite having a size chart, clothing tends to run 1-2 sizes up or down from what it should. How? If a pair of pants you call an XL normally has a 36" waist, they should have a 36" waist. If you produce an XL and it somehow has a 32" waist or a 40" waist, you need to call that a different size.
I have never bought clothing from Pinup Girl that was the size it claimed to be.
They don't really take returns or exchanges. The prices are exorbitant for how poorly the clothing is made. They police their reviews on Facebook and their website so you can't actually tell anyone how the products are made. If you bring up any of this in the Facebook group, you get explicitly told how much they don't care about customer feedback.