Frankenstein and Walton are not reliable narrators because their personalities, perspectives, bias and personal interests which could impact how the story is recounted. 

Unreliability in narration is evident between the two perspectives of Frankenstein and his Creation. Due to different perspectives, their stories have some similarities but many differences. 

In Walton's letters he mentions he was once a failed poet. This demonstrates possibility inaccurate retelling of Frankensteins biased story of his life and creation.

The fact Frankenstein is able to recite word for word the letters from Elizabeth supports why as narrators he is unreliable. Walton would not have took notes during the conversation and therefore overtime created or changed ideas based on his schemas and filling in the unknown, or changing words more common to his understanding. 

Manipulation or emphasis of events which occurred is easy to do. Throughout the novel Frankenstein may have altered the story to make others feel sorry for him or believe his opinion.

It is almost impossible to convey how someone feels. For example, when Frankenstein and the Monster/Walton and the Monster meet it is difficult to describe how the monster was feeling (unloved and separated from the rest of the world).

I do not think Walton and Frankenstein are completely reliable narrators as their outlook on the Creature’s actions are biased and discriminatory. They do not give sympathy or try and understand the perspective of what the Creature is trying to convey through to them. Both the accounts from Walton and Frankenstein often portray the Creature as something that is “hideous”, and they seem to overlook the fact that unlike what they perceived, the Creature did have human-characteristics, especially ones such as love and longing for as sense of belonging. The creature strived for acceptance into society, but his appearance constantly hindered this desire, and he was left rejected by everyone, including his own creator. Frankenstein particularly appears to disregard this, and instead emphasises on his problems and what effect the Creature’s actions have on him, rather than the other way around. Both Frankenstein and Walton narrate their side of the story to generate compassion and sympathy towards them, and this results in an unfair impression of the Creature being created and depicted. 

Frankenstein gives an account of his story regarding the creation but allows his biased emotions to cover the true logic of the events. He had a fixed opinion that his creation will be destructive to the human kind. On his deathbed he tells Walton that he is concerned that without him destroying his creation, the creation will ‘live to be an instrument of mischief’. In contrast, the creation confesses to Walton that ‘neither [Walton’s] nor any man’s death is needed to consummate the series of [his] being.’

Walton on the other hand, is reliable because he is only writing down what he sees and hears. He is clearly aware of when his emotions may overtake his truthfulness and warns the reader. An example of this is when he encountered the creation. He is willing to hear his side of the story and ‘when [he] called to mind what Frankenstein had said...and indignation was rekindled within [him]’, he writes this quote down to warn the reader.