As I market my services to various clients from various backgrounds, I'm always trying to come up with a unique value proposition that communicates to them. It's not that I want to appear superior to their alternatives, but I do want them to understand what makes me unique. Sometimes I use
"Hiring an experienced software developer who knows what their doing before they start is much more cost effective than paying someone else to learn"
which works well if a customer is interested in completing a project and are not making an investment in someone else's capabilities. Sometimes I use
"I know how to go straight from point A to point B while some are good at talking about going from A to B and others are like to start on the path from A, get distracted and take twice as long to get to B. I have a laser like focus on the task at hand"
which works well if a customer has been disappointed in capabilities of another developer or development team. Sometimes I use
"My experience with 50+ projects in 10+ industries has given me insights about how those businesses are run that might provide value in unexpected ways to your project"
which works well if a client is unsure that I can complete the project using a new toolset or technology.
I see now that you cannot have one unique value proposition. Every situation, every project and every client is different. Not only are they different, they are unique. I also see now that I am not a salesperson applying a closing method. I'm there to listen, learn and offer something of value. If that means I have to be honest with someone, rather than packaged, so be it.