Bad fuel -- how can you tell?

This question isn't necessarily specific to Tacomas...

Any tips on inspecting fuel that is potentially bad? I know the obvious things to look for, such as water contamination and debris in a sample jar ... but what else should one look for? I've heard that fuel that feels oily and doesn't evaporate quickly is a bad indicator. I also once heard an old school heavy equipment mechanic say that the fuel "tasted like bad fuel" after he touched a drop of it on his tongue, but I couldn't tell if he was being serious or pulling my chain.

So...any advice?

 

Gasoline that feels oily and doesn't evaporate is a bad sign. If it smells like varnish and has turned dark is an even worse sign.