Several texts talk about malicious/dishonest verifiers in a zero knowledge interactive proof but none of them properly detail how a dishonest verifier can gain extra knowledge over a honest verifier using some example like Quadratic Residue Interactive proof or graph 3 colouring Interactive proof. I went over the proofs for these 2 examples for honest verifier where obviously no knowledge is gained, but I am unable to figure out who this breaks if the verifier were dishonest. I assume by dishonest, it means a verifier who doesn't use a random number where he is supposed to or is my assumption wrong? For e.g. in the QR proof, the verifier is supposed to pick a random bit & send it to the prover - but let's say he doesn't pick a random bit but always sends 0 or always sends 1 - how does this give him any extra info in any way?

Several texts talk about malicious/dishonest verifiers in a zero-knowledge interactive proof but none of them properly detail how a dishonest verifier can gain extra knowledge over an honest verifier using some examples like "Quadratic Residue Interactive proof" or "graph 3 colouring Interactive proof". 

I went over the proofs for these 2 examples for honest verifier where obviously no knowledge is gained, but I am unable to figure out who this breaks if the verifier were dishonest. I assume by dishonest, it means a verifier who doesn't use a random number where he is supposed to or is my assumption wrong? 

For e.g. in the QR proof, the verifier is supposed to pick a random bit & send it to the prover - but let's say he doesn't pick a random bit but always sends 0 or always sends 1 - how does this give him any extra info in any way?