Buyer backed out after our MM became available. Is this allowed?

We both agreed to a trade and arranged to use a trusted MM. We waited until the MM became available, but once they were ready, the buyer said they no longer wanted to continue because they found another seller. This wasted both my time and the MM's time. Has anyone experienced this before, and does this violate Rule 9?

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u/Jeannyla — 6 days ago