What Unique Sales Proposition USP could be offered to customers who would use a wedding planning service?

Try using a Free 20 minute Consultation promotion perhaps and create a map of questions you will ask and answer with your potential customer during that consultation. It will be up to you if you want to mention the value of such a consultation and it may make sense to not mention the price if your price is somewhat in the higher market range.

Consultation can be anything from basic wedding planning to menu planning and so forth. I am sure there are more ideas you can come up with, but I think it would make sense to give free consulting. Make sure you make that map of what you plan to discuss so you don't exhaust yourself, efforts, and time.

Emphasize in all your marketing communications the importance of a good wedding. The lifetime of memories that rely on GOOD planning.