Foxart is correct and furthermore Colorado upholds verbal agreements as legal binding contracts just like written contracts. Might be worth the hassle of pursuing but I leave that to you as you might think it not to be worth said hassle. As I mentioned before, I would NOT have been so cordial about it and most likely hearing about "specfic performance" from a friend (like foxart mentioned here) I would then most indubitably would go after the guy for his bike he had promised to you in the first place for $5.5k and force him legally to uphold his side of the agreement. That's just me but I digress.
Attached is a photo of verbal contracts. Looks like it was posted with a recent date of 2017. Might dig deeper if you decide to move forward to make sure that law is still viable today. Again, I leave that to you Southpaw.