There's very little that the seller's agent can do, about a no-show agent, other than to call them and let them know that it was unkind.
Sellers spend time preparing their homes for showings (vacuuming, lighting scented candles, febreezing to remove last night's Halibut dinner, taking the dogs to the neighbors) only to find that the buyer's agent never shows. It's incredibly rude.
Sometimes, as a buyer's agent, we find that "missing" a showing is unavoidable... running late... maybe the client was a true-no-show, maybe a child got ill, but that's no excuse for not calling to notify the seller's office/agent and let them know.
The seller's agent has to walk a fine line, in chastising the offending agent, since they're going to have to continue to work with this agent, and hopefully have them show their properties in the future. If this agent is a repeat offender, the seller's agent can determine if it makes sense to ban them from their showings. But they would have to be a repeat, repeat, repeat offender, in my opinion, to warrant such a ban.