This might just be the policy of your individual store, but (in general) men are actually allowed to work at Victoria's Secret as Cashiers. They are not allowed to be bra fitters, however.
I wouldn't feel comfortable with a guy telling me that i look great in something when i'm half naked. xD To me It would seem like the guy is just using this job to stare at womens boobs and stuff all day. xD Also my fiancé would be pretty uncomfortable knowing that a guy is seeing me in something intimate (bra and undies) and telling me what looks good xD.
At Victoria's Secret they measure your breast size so we know what size bra to purchase. This is not only uncomfortable for woman.. But did it ever occur to you that TEENAGE GIRLS shop there? It would make you look like a pedifile. And it also would make girls feel very awkward.. When they shouldn't in a store made for just girls
Ahaha do you know how awkard it would be if a guy was measuring our breast size or telling us which underwear is what. It's just super awkward.
I don't think girls would feel comfortable buying underwear from a guy.