1. Roadmap/Design/Mock up phase(maybe with 3 different mockups and a couple revisions)
2. MVP - work on must haves first
3. End User Feedback - add/remove features based on End User Feedback
if the customer built the perfect product stop here...lol...
4. Customer Approved Product
You might also want to explain no project is guaranteed to work. All you can do is minimize the risks and costs. by making as many mistakes on paper and mockup first and realize that ultimately it's the end users decide whether it's a good product or not. And anyone that says any different is promising rainbows and unicorns.
If you really want to knock their socks off offer to identify frameworks, libraries, templates, third party products and apis to minimize cost and time to get the project completed faster and with less overall costs.
Now your starting to move into trusted advisor territory.