usually the replies but sometimes nothing salvage a truly shit op
First, you ask all your friends what they think about it (if unable due to time constraints, ask yourself what would they think).
After asking, see how the thread is chugging along. Some topics may tend towards kuso, but not all of their instances are. Judge fairly.
Then weigh the souls of the thread's posters. If most of the souls are heavier than a feather, it's definitely kuso and you should spam the thread.
If friends cannot be located, it is possible to imagine them up and then ask them or ask yourself to imagine what they think.
However, your friends are here.
Usually, the biggest red flag of a thread being kuso is an overenthusiastic adherence to the zeitgeist.
Secondly, an interference with the Wa (和).
Thirdly, contextual belonging.
Finally, depth and/or meaning to the thread.
These are the four great pillars of thread posting (スレ立て大四柱). A perfect thread adheres to all four. Quality decreases as one of these principles is forsaken. A thread's kuso level depends on how deeply one adheres to these principles but as a general rule if only two pillars stand then you're likely in the presence of a kuso thread. In the current age (eternal lost decade), very rarely will you see a thread that adheres to more than one pillar, and it's usually only the pillar of contextualism.