After a few years of debating chiasmus here are some suggestions to discern a genuine  from an imagined pattern.

• The section of scripture is defined by repetition of key words/phrases i.e. bracketed or book-ended.
• The pattern is characterised by  repetition of keywords, and phrases or by opposites (chiasmus based only on concept rather than exact repetitions are more difficult to agree on).
• if key phrases are inverted (“heaven and earth” v “earth and heaven”) this is strong evidence.
• The chiasm has a balanced symmetrical shape.
• The centre – often a regular parallelism – is highly significant.
• the whole unit makes sense.
• the unit respects other textual features.
• Broken patterns may nonetheless be significant.
• The pattern becomes clearer in the original language.