Unreliability only works if it is discoverable. The audience has to be able to reconstruct what happened from evidence the piece supplied, otherwise the reveal is the story admitting it was misleading and expecting credit. The rule is that a second viewing should come out more coherent.
The interesting versions are not lying. A narrator who is self-deceived, limited, or defending themselves is the useful kind, because the gap characterises them. A narrator who is deliberately deceiving only tricks the audience.
In commercial work the honest application is the testimonial where somebody is plainly describing their own behaviour with a generosity the footage will not support. It is charming, and it convinces in a way a perfectly consistent account never does.
What is an unreliable narrator?
A narrator whose account the audience comes to doubt. The gap between the telling and the events becomes part of the meaning, usually characterising the narrator while it misleads the viewer.
What makes an unreliable narrator work?
Discoverability. The audience must be able to reconstruct the truth from evidence already given, so a second viewing comes out more coherent.