In addition to the 4 Guidelines above, it would be helpful if Audiogon added the others they are using as a basis for deleting posts. Of course, they can do what they want. But, if posters were aware of the other, as yet unspecified Guidelines, they may frame the posts differently - to avoid removal.
Sometimes posts have good information that mysteriously disappears.
Of course some posts clearly warrant removal - the posters know it up front. That won't stop.