It seems you are using 'seeming smart' as interchangeable with 'convincing' or 'persuasive'?

However, these are quite independent. Someone can easily convince me of something, without my thinking they are more intelligent than I am, and without convincing me that they are more intelligent than they are.

Consider a 'smooth talker'. I think people generally recognize that these smooth-talkers are more likable and persuasive on any topic, but there is no necessary correlation with having a higher IQ. In fiction, there are extreme examples like Forest Gump (low IQ, very smooth) and innumerable moderate examples like Peter Venkman in Ghostbusters. Whereas intelligent characters are often portrayed, though not always, as not very persuasive.

...Smooth-talkers and scammers will often break-down defenses by signaling equal intelligence when they actually have higher intelligence.

In the example you gave, how do we know Velikovsky wasn't very intelligent? (We do know he had the ability to write very well, to make a false history seem true.) My question isn't that he is or wasn't intelligent, but whether his deception of Yvain was due to Yvain over-estimating his intelligence.

..Can you think of an example (a fictional one might be easiest) where a deception (or even any conflict) was actually about someone overestimating someone's intelligence?