When booking these services with a company, often you may wish to have a particular photographer/videographer and DJ for your wedding because you have seen their work or heard their play style and really like it. Make sure this is detailed on the contract with the person’s name. Again, also include the clause that if that particular person is substituted, you will not pay for the service and will receive a refund on all deposits.
This happened at our wedding with the DJ. The one we were told was coming and who knew how our ceremony music was laid out did not show up, and the substitute DJ that showed had no idea how the wedding service was to proceed with the music. There was a mess up with some songs during the ceremony and we had no recourse, as we didn’t include that provision in the contract. So be aware of this. Don’t pay for a last minute substitute (unless you were thoroughly happy with their service).