The answer to what will trigger a decline in prices is “time.”
Daily news stories about how bad things are, brown lawns while driving around, weak sales, builders losing money, it will add up over time. Buyers can hold out and have a lot readlily available advice to do so. Builders, forclosures, arm resets and people falling behind no longer have that luxury, they see time as working against them. Patience young Jedi, Patience.