There are multiple approaches to Real Estate Associate access to a building. The Owner has the right to list and show their unit to prospective purchasers. The Board should not interfere with the process, however for building security, it is possible that the Board can put in some guidelines, but the cannot be so restrictive that they would hinder the sale of a unit. I would think that the Owner should be able to provide access to the building for a prospective purchaser to view the suite
The Real Estate Associate should check with the Property Manager to find out where they are permitted to put their lock box and if there are any other guidelines that are in place.