They would be premitted to enter with reasonable notice to you, however when they enter without notice they are trespassing, and potential engaged in a constructive breaking an entering.
You are paying rent, and while still a tenant you have the exclusive right to the interior of your arartment.
Explain this to your "friendly" Realtor, or contact me, and I will explain it him/her that under no uncertain terms will he/she EVER show up in your apartment ever again.
Glenn F. Russell, Jr.
Law Office of Glenn F. Jr.
38 Rock Street, Suite #12
Fall Rive, MA 02720