The date is the stock. A double booking here is not an annoyance but a reputation, and a diary that blocks an enquiry instantly prevents it.
The deposit separates an enquiry from a contract. With no money paid, a date is reserved and free at the same time, and the software has to display exactly that state.
The contract is nearly identical from party to party and differs on three points. A template plus times, address and equipment produces it in two minutes instead of half an hour.
The tech rider belongs to the date and not to anybody's memory. What the venue supplies and what goes in the van decides loading time and two full hours of setting up on site.
The host's music requests are a document with a deadline. A list closed a fortnight ahead removes the argument on the night itself.
Fellow DJs are part of the operation. Passing on a date you cannot cover needs a record with commission, or the revenue vanishes into a phone call.