The economics that shape the process
A travel enquiry is unusual because a serious reply is expensive. Building an itinerary means researching options, checking availability, pricing components and assembling a document. That is an hour or more of skilled time, spent before any commitment exists.
Every process decision follows from that fact. The purpose of qualification here is not to filter out people you do not want to serve; it is to decide when to spend the hour. An agency that quotes everything in detail is either working unprofitably or producing quotes too quickly to be good, and both are visible to customers.