This is a problem I've been running into in bridal shops actually. I'm trying to find a dress at the moment and the bridal shop person is always telling me to put my hair up so I can see what it will look like on the day. When I tell them I intend to wear my hair out loose they're always aghast! "But of course you'll wear it pinned up" "it really wouldn't look right out loose with the neckline you want" I had one person insist this at me so much and then every time I was behind the curtain getting changed she would go on at my friend about how wrong I am to want my hair out loose.
I never ever have my hair up and I want to be comfortable and look like me so I won't have my hair up on the day. After lots of attempts at gentle persuasion to drop the subject I just had to say "Look, forget about my hair, it's not anything that needs to be decided now. I'll pick my dress and then decide on the hair closer to the time. You need to back off." She looked highly insulted and it may not have been the right way to say it but if I let her keep badgering me I would have ended up in tears.
This should go in a manual for sales people on "How to Lose the Sale!"
Really, how hard would it have been for her to say something like, "Oh, that will be fresh and different! You have such lovely hair, I think this dress would go well with your hair down."
As for how you handled it--I've been in similar situations with salespeople who would. not. stop. pushing their agenda. My feeling is that if you've tried politely to shut them down a couple of times, then they are going to get what's coming to them. Not that I'm rude, but I definitely get firm. And I stop asking and start telling. "You need to stop telling me that. I'm not changing my mind," isn't rude. It can be said rudely, of course, but the words themselves are a statement of fact and not, in and of themselves, rude.