There are a couple reasons you'll almost never get your money back selling a Warmoth.
Warmoth only sell parts. They aren't a finished instrument manufacturer. That means no one knows what kind of care and attention YOU put into your guitar. On top of that the general guitar playing populace has no idea about Warmoth. Sort of a double whammy. People like to stick with well known commodities, a Warmoth put together by some random guy is a huge risk.
Then if you examine the people who do know about Warmoth, sort of a different side to the same coin. Even if I trust the parts manufacturer, I have no idea about your workmanship.
Also any of us that do know about Warmoth know that it's real strength is customization. So for us a lot of the fun, and practicality is that we pick and choose within our budgets to come up with as close to an ideal for us end product as we can. You would have to move off the price you paid by a nice margin for me to think about your project. presumably you picked out parts for yourself, not me. So if you offer the same price (let alone any kind of mark up,) why would I not just go to 'W' and browse away till I found something i really love.
This also begs the question, if the prior owner went through the selection process, and made his dream axe, what is wrong with it, why is he selling?
Warmoth buyers are usually inclined to do most of the guitar work (some paint, some don't, but most assemble, and solder,) so they're not as inclined to want to compensate you for labor they would cheerfully do. In short, Warmoth totally fill their niche. They do such a great job filling the needs and wants of their customer base, there is no way for a 2nd hand market of their goods to thrive. Brand name guitars depreciate a lot, with a few notable exceptions. Off brand stuff is doomed to a price plummet. Warmoth turns quality part after quality part. No scarcity to drive demand.
You might have the greatest guitar ever, but I can also build the greatest guitar ever, and it will be tailored to my wants. makes a tough sell.