The interview includes process questions, asking about certifications, and other factors like years in business, licensed & bonded, uniforms, or other specific concerns.

For software though, imagine freelancer.com, but there's an agent actively soliciting feedback, not just a one-time post and nothing happens (or someone else gets picked).

The rejection reply could still have useful info, like "We chose X instead based on their [experience, number of ratings, answers to questions like Y, Z]. Thank-you for your response to our request!"