How would anyone be able to buy a bra, which is an elastic device that lifts, shifts and holds the breasts – an incredibly variable bit of anatomy – without trying it on?
https://www.google.com/search?oq=can+you+try+bras+at+store...
I would assume this company has a marked bunch as having been tried and sends those out first and they are marked as 'trial' bras.
Boxers go against your asshole. Bras, not so much. Women's swimwear – very fit dependent – includes a protective, throwaway panel for this purpose.
Tons of women's clothes are highly fit-dependent. Boxers mostly aren't.