The Q: My florist says that she won't create a sample of my bouquet. Is this normal or is there a problem? Also, if it's normal, how will I know if it will be what I want?
The A: It's normal. I know it seems awfully like leaving a lot to chance, since it's in like, nearly 1/2 of your photos, but because of the labor involved in putting together a bouquet, it's a practicality and cost issue.
So, what should you expect then as some sort of re-assurance? I personally like for the florist to at the very least have 1 of each kind of bloom they are suggesting for the bouquet (unless it's SUPER short season, like a peony, for instance) in house when you go in to discuss the centerpieces. This way you can get a sense of the textures of the flowers, at the very least.
What we like to do here (particularly if a bride doesn't have a very strong sense of what she might like for her personal flowers) is to go with them to the flower market to show some of the variety and pull some things together. You should have shown the florist a photo of your dress prior to doing this, but it can be a lot of fun and very helpful.
The BEST and simplest way to get what you want, even with the above actions being taken, is to clip photos of your top 2 or 3 bouquets that you've seen in magazines or online. This gives the florist a sense if you want something soft, or romantic or graphic or sculptural.... You get the picture.