A Missouri jury goes after the real-estate industry’s commission structure. Here’s what that could mean for homeowners.

A Missouri court found the National Association of Realtors and two real-estate brokerages guilty of conspiring to inflate real-estate commissions, a decision that will likely have a deep impact on the U.S. housing market.

The NAR, one of the largest industry groups in the U.S., as well as brokerages HomeServices of America and Keller Williams,…