User blog comment:JustSomeDude.../712 - The Implication/@comment-4754162-20130627160513/@comment-4899461-20130627162030

It's based mostly on Doflamingo's reaction to his discussion with Law in Ch. 697. It's the first time we've ever seen him stressed out about something. And when Law asks him what will happen if he cannot provide Smiles to Kaido, his face becomes so strained that Buffalo notes it in fear. He also gets the most angry we've ever seen him as Law hangs up on him.

And if he wasn't afraid of Kaido, he wouldn't have gone so far to get Caesar back. He was willing to lie to the entire world, including the Marines and Admirals, in order to get Caesar back. He wasn't afraid of what the government could do to him. He was willing to lie to everyone and get on their bad side, except he did not want to get on Kaido's bad side. The only reason for that where he would react to Law in such a way is true fear of Kaido.