Well, it is irreversible to the extent giving any physical papers to another person is irreversible.
However, the upside of driving your Tesla with a case full of bills is that there's no immutable world-wide distributed record of your transaction making it irreversible.
Sure, you could claim that, but if you're doing it at a scale that ultimately matters, then you're only harming yourself. The only kind of people who would be interested in having business with a person mired in such controversies are people you don't want to have business anyway.
We can spend all day coming up with slight variations of this scenario where one or the other person is to blame.
In the end, this situation is one of the few things humans have grown really adept at handling. We're (compared to many other things) very good at negotiating complex social situations and teasing out who are getting shafted in a situation, and we have techniques for dealing with it. (Spreading rumours and/or going to the local leader are prominent among them.)
We have set up economic systems based on trust since forever, and they generally work very well. The only times they stop working are when too large authorities get involved. But there are many responses to that that aren't cryptocurrency.
However, the upside of driving your Tesla with a case full of bills is that there's no immutable world-wide distributed record of your transaction making it irreversible.