So, some of the information on the JoS is seriously out of date, a mismatch between legitimate experiences HPS Maxine had with a Demon/God, information from occult texts and grimoires most of which is half truths at best, research into the Ancient Religions which is mostly true but also very allegorical and that which was dictated by Thoth directly, essentially the only information we know is 100% correct is the information from HPS Maxine and Thoth, the whole gambling house thing I assume is from the grimoires as it wasnt dictated by Thoth nor did HPS Maxine state it was told to her and as you say its somewhat strange so I assume it came from a grimoire.
The Demon/Gods section is due a rework but it takes a tremendous amount of time as its pretty much all being done by like 3 people for the purposes of keeping everything true specifically to avoid situations like this in the future.
How I determine credibility is through falsification e.g, if it dosent work its probably not true, thats why I know Satanism is real, the very first time I performed a very old fashioned ritual we used to do based off the runes I felt an energy feedback so strong so powerful it left me gasping for like 30 minutes, every time I perform a God's ritual now I feel incredible waves and I do mean literal waves of energy radiate from their sigil afterwards, at a certain point it became irrational for me to not have faith.
There are mantras and words of power that once used cause an immediate physiological reaction, its not a matter of belief when one experiences these things I have healed from wounds my doctor assured me would require surgery.
The truth is not every source used in the JoS is 100% factual as the whole thing was basically a one woman job and so some information comes from bad sources HPHC himself acknowledges this and is working to change it but the enemy texts had to be read to simply learn the names of certain Demons and their sigils with those texts came half truths and lies but it was necessary for us to get our feet on the ground so to speak even if some sources were wrong, for instance I really doubt Demons gamble, seeing as how they can literally see the future and they don't use money so it would be weird if they did, but everything that came from Maxine directly has been proven right time and time again.
So why believe? Dont believe, see for yourself. Perform the chakra opening meditations and see for yourself the feeling of your own soul, once thats done done work from there, here is a really easy way to feel the reality of our Gods, do the foundation meditation (once you have opened every chakra) do the foundation meditation for like 30 minutes, saturate your soul in energy to the point you can easily feel that energy and then think in your head "Lord Satan I tribute my energy to you, please accept" and you will literally feel the energy be taken from you and it takes very little advancement to sense this and its a very easy way to confirm the existence of the Gods.
But the truth is you aren't going to find definitive written 100% undeniable physical proof written in some book somewhere, Satanism is fundamentally an experiential religion, Satan explicitly guides us without a written book, this is intended, we aren't meant to have every answer, part of our path is figuring things out both as a community and as individuals.
As for moral principles, we base our ethics primarily of Ancient Greek moral philosophy so think Aristotle, Plato and Socrates, the JoS ethics page expands upon this more directly but reading the works of those three authors will teach you much of divine morality at least for the purposes of a Human.
Its really good your asking these questions, a questioning mind is a Satanic mind, those who adhere to dogma never escape the slave religions.
Only in Satanism do we say that you will see the truth without paying, without relying on faith, without doing drugs just by meditating, worst case scenario you waste a few weeks, what do you have to lose?