As an ex-founder, I've had VCs reneg on term sheets/handshake deals several times before. This is commonplace.
I now treat VC as a funny form of enterprise sales, and this happens there too. Want a 6/7/8 figure deal? Same thing: has the group bought stuff at that level before, if so, what is the process? And, the more critical the deal, the more imp. you talk to folks who also recently ran the gauntlet.
From experience its a very small marketplace (esp with big checks). So there is a very high expectation that people act with longterm consideration of one another and subsequently their reputation. Just disappearing, or changing terms without a material change is dishonest period.