Is it possible to do a divination and see whether a being would help you if you approach them?
One of the common methods used for that type of question is the pendulum. You would hold it above the seal of the spirit in question and ask it if the spirit would be willing to work with you.
Oooh. Noice. Thanks for the answer.
This is exactly how I learned that Belial was a guardian of mine.
I went through all of the seals using a deck of flash cards that have each Goetic spirit on them. With the exception of Vassago, the pendulum was dead or swing ‘no’ until I reached 68 - Belial. The pendulum swung in hard circles over his seal. I continued all the way through until 72, but again, all were non-responsive or ‘no’. I went back to Belial’s seal for confirmation. Again, wide, almost violent circles. It was a hint and a half.
Been giving him scotch and Swiss chocolate during evocations ever since.
I definitely endorse the pendulum method for establishing this sort of thing.