As long as I stick to certain brands that I have gotten to know I am ok but once I switch brands all bets are off.
My wife explained women’s sizes to me and I came away with a great appreciation for the misogyny of the universe.
First, It boggles the mind that the dimensions of an outfit could be reduced to a single number, and second that this number can have no fixed relationship to size other than a vague monotonic function that is particular to a given brand.
As a man I am privileged to just enter 36x30 into the pant size and I’m done.
And all of those women are probably reporting correctly its just that since each brand is different each women’s expectations are also different.
Those in the first group were used to a brand that runs about the same as this, those in the second group are used to a brand that runs bigger and those in the third group are used to a brand that runs smaller.
I’m surprised this hasn’t been overcome by market forces. One would expect that the first designer who actually gave their clothes dimensions would make a killing.
My daughter was just commenting on this the other day. She saw a dress she thought was cute, but according the the chart, 2XL = size 12!! 
Back when I was a teen, size 12 was considered average - right in the middle of the “Medium” range. XL started at 18. These days, who knows??
I’ve had the same experience with pants. All the tags have the same size printed on them, but they range from can’t-button to won’t-stay-up-even-when-buttoned. Weird.
Yes, they go through a process to re-tag/bag/steam/etc. and sent back into inventory as new, unless there is a QC issue with the item.
Most e-commerce apparel companies operate around 20% to 30% returns due to sizing and fashion reasons primarily. If you are under 20% you are doing good.
When I worked for QVC (and that was 10+ years ago), QVC had standard (for them) size molds. For example, they had a “QVC size 10” mannequin. And if you as a vendor sold a dress on QVC, what you sold on QVC as a “size 10” would fit that mannequin perfectly. If it didn’t (and QVC didn’t care what your excuse was), well then QVC simply wouldn’t sell your product.
The result was that women were perfectly content to purchase their clothing on QVC, because if (say) they were a QVC size 8, then everything that QVC sold as a size 8 would fit them perfectly. Worked fine for QVC, worked fine for their customers.