I definitely relate to the basic issue of estimates with my one-person consulting projects. The bit they didn't mention is: who pays for the cost of the inspections and analysis? In software, it can take a long time to analyse the requirements and the solution, in order to come up with an estimate (or fixed quote), and I find it awkward trying to get paid for that time.

Do a roadmap. Fixed scope small project that you get paid for where you define requirements. Deliverable is a functional requirements doc. It derisks the project for them, and gives you more confidence when quoting a fixed scope fixed price project. You just don’t guarantee timeline. I’ve been doing it for over a decade - it works wonders.