Of course, one can allow a character like that to get his comeuppance with his behavior. But I wouldn’t let myself be caught up in false ambition. Look at the property, reflect on the price, and also consider that at least one neighbor will no longer be a friend. And then buy it or not.
If they are now asking for €140K and the neighbor thinks of putting down €100K, he’s already screwed. He will get his plans thwarted, whether by you or someone else. I would make the agent aware of the neighbor’s behavior. That will likely trigger a bite reflex in him as well, because he would be left empty-handed if the sale went to the neighbor (property known before the agent became active).