One of the techniques I used to use when I was shooting weddings was to publicly announce to the crowd that they would be welcome to take any photo they wanted as soon as I finished, and then when I did finish with a particular pose or grouping, I'd ask the subjects to pause for a short while so the other people could get their shots.

Generally speaking this meant that people would respond respectfully, and I could control the pace and scheduling of things. In essence, I was depending on the fact that my vision, technique, equipment and materials would result in a superior enough product that my customers would pay me for extra prints in preference to just getting copies of their friends/relatives' shots.

It also had another benefit - I was rarely lacking for cooperation from the wedding guests, which meant good results when I shot candids, and sometimes an extra helping hand or two when I could use one.