The SMS Power-Up offers a 1-way SMS push notification system for updates and alerts to both clients and staff.
When you send SMS messages, every message automatically has your business name inserted at the beginning of the message, and a footer line at the end that says:
"No reply | Msg STOP to opt out"
So, while they can physically send a reply if they were to try (as this is required to allow for opt-outs), the footer is intended to let recipients know that replies to this number are not monitored.
From what we've seen to date, this footer is very effective in communicating that they are receiving messages from a non-monitored number, not intended for replies, as we almost never see recipients trying to send SMS messages back.