It is good practice to have transparency in status of stories committed in sprint backlog
Sprint review, second last important ceremony in the sprint. As per scrum guide, “The purpose of the Sprint Review is to inspect the outcome of the Sprint and determine future adaptations. The Scrum Team presents the results of their work to key stakeholders and progress toward the Product Goal is discussed. “

Every sprint team’s deliverable may not be the same. Sometimes team is able to complete the committed work, sometime they may not. When team not able to complete all the work, team feel hesitant to showcase the incomplete work to customer. As a result, they want to defer the sprint review. This situation becomes difficult for scrum master to handle. He wants this ceremony to happen in sprint duration only. Conversely team not ready for demo. So how scrum master will handle this situation ?
I think it’s OK to just showcase completed stories only. Therefore scrum master can have discussion with team. He can convince them of showcasing completed stories first. Next team just talk about incomplete stories. What challenges team was facing and why could not complete the stories. Next team discusses possible timeline to complete and showcase the pending stories.
It is always advisable to demo completed stories. Hence try to get feedback on completed stories and notify customer on incomplete work. On the whole, have the status transparent with customer and stakeholders. Team should have complete transparency with stake holders. There should not be any dark work.
Further Action
Team should review the cause for incomplete stories in retrospective. Team should review whether it was due to overestimation or some blocker or some other reason, due to which team could not complete all the committed stories. Accordingly they should have improvement actions decided for further sprints.
Hope this will help you to guide your team on handling incomplete work in sprint review.