Even though there are problems with our perceptual systems, this doesn’t mean that knowledge gained from our senses is completely unreliable.
Knowledge gained from our senses may not always be unreliable. Just like many natural sciences, if you have enough trials, you can detect the reliability. In this case, if you have multiple witnesses that all give the same result from their senses, one can infer that the knowledge gained is reliable. Although even from individuals, we can assume that the knowledge gained from our senses is not completely unreliable.