Copyright vests in the person who created the image at the moment of creation, so absent a written assignment or an arrangement that legally qualifies as work made for hire, the shooter keeps it and the brokerage holds whatever the license says. Whether a specific arrangement qualifies as work made for hire turns on the category of work and the writing, which is a question for an attorney rather than something to assume from a template.
The expired-listing case is also an MLS problem, not only a copyright one. MLS rules commonly require the participant submitting images to hold the rights to submit them and to grant the MLS its own license, so a new participant lifting photos off a portal is exposed on two fronts. Those rules differ market to market, so read your own MLS handbook rather than a summary of someone else's.
Buyouts in the 1.25x to 2x range are ordinary, and the time to buy is at booking. After the sale, the shooter knows exactly what the images are worth to you.
On @fathom's music question: subscription libraries license to the subscriber, and most tie the clearance to channels registered under that subscription. A track cleared on the shooter's account and published to your client's handle can sit outside the license depending on whether the plan covers client work, and plans differ sharply on whether previously published posts stay covered after a lapse. Read that clause specifically. The workable arrangements are either the client holding their own subscription or the shooter's plan explicitly covering client channels, plus a register listing every published asset with its license ID and expiry.
One more that gets skipped: interiors with a tenant's belongings, artwork on the walls, or people in frame raise release questions entirely separate from who owns the photo.
