If a girl does a lez scene just because it's less disgusting than having to touch a dick then the scene will suck.

If a girl does a lez scene because she's hot for the other babe and is into lots of wet, sloppy tongue action, that's probably hot.

A little enthusiasm and into-it will overcome lack of a cock, iffy lighting, questionable camera work, etc.

If the technical details of lighting, sound, etc are perfect but the girls are mentally rehearsing cashing their check then you wind up with a Vivid scene.
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"If they can't picture me with a knife, forcing them to strip in an alley, I don't want any part of it. It's humiliating." - windsock