Another good example of a firm that is notoriously dishonest about term sheets is Global Founders Capital (the rocket internet people). They are known to blow out rival firms offers financially and then after everyone is out, come back and try to renegotiate at more onerous terms.
1. Some people that have real-world experience with raising money and term sheets. They understand what the norms and expectations are in addition to understanding the legal aspects.
2. Other people that lack the real-world experience and are just speculating without understanding the norms. They are only referring to the legal aspects.
You can use all the tools of the law to disadvantage others but word will get around that you're a dirty dealer and it'll be their privilege to not do business with you anymore.
The two firms are essentially dictatorships masquerading as firms. What you get is a bunch of definitionally impotent lieutenants who go make deals and carry them to the 1 yard line and then the boss (Masayoshi or oliver) decide again as if nothing had happened before whether or not to execute.
Unless the bosses are the ones leading the deal, know that you there is zero good faith and a lot of risk as far as outcome goes.
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.