Be firm in rejecting. I think alot of us face this: Pushy sales people. If possible, get your SO to go with you. Chances are that if you go yourself, you may be tempted to get the package and give in. I feel that generally females are very prone to impulse purchase, myself included. I once put down a deposit for a pre-wedding photography when my SO was not there with me, after that i felt so regretful, that money could have been better spent. Although it is a few hundred only, it is still money.
Going with SO helps you to be more firm, guys are mostly very logical in their thinking and will help you to pull away from the salespersons when either of you are not comfortable with the package or the boutique. You also need to consult your SO about it anyways, since he will be your hubby to be. All the best in your boutique search dears!