For the cake thing, the simplest thing in my mind to do is to have a catalog.
And for the wedding cake part of the catalog, you simply do not offer customization: to include cake toppers and names on the cake.
(Same thing, I guess, for the anniversary cake part of the deal as well)
In other words, do product sales only. Period. If it isn’t in the catalog, you don’t do it. Period. No substitutions that aren’t listed in the catalog.
More challenging would be the wedding photographer. What I would do in his/her situation is to draw up non-exclusive agreements allowing him to provide services at select churches. Then he could select the churches where he’ll provide wedding photography. So he has arrangements with Father Smith from St Mary’s Catholic Church, Father Jones from Christ LCMS Church, Brother Carson from First Baptist Church, Pastor Mason from Westminster PCA Church.
So if Bob and Mary come in to schedule photos for their wedding at St Mary’s, no problem. However, when Lloyd and Lance come in to schedule the photographer for St Judas Iscariot Episcopal Church...the photographer can truthfully tell the couple: “Sorry, but I only do wedding work with churches where I have formal written arrangements. I’m afraid I don’t have such an agreement with St Judas. Perhaps I can refer you to a photographer who does. Or if you’re dead set on having me shoot your wedding, perhaps you could talk to Brother Carson over at First Baptist. I’m sure he’d be happy to let you use his church for your affair. Once you bring me appropriate documentation from Brother Carson, I’ll be more than happy to have a consultation with you.”
What about Bob and Mary who are not having their wedding in a church? Where do you fit that in your scenario?