In terms of what agents can and cannot do while sheltering-in-place regulations remain in effect, summarized below is the guidance from the NY State Association of Realtors:
In-person showings are forbidden. This applies to showings of vacant properties.
Agents can enter a vacant home to take photos.
Agents should not travel to unlock a vacant property to allow a buyer to do an unaccompanied showing.
Agents should not be involved in coordinating unaccompanied showings. Buyers and sellers should coordinate on their own.
Agents can provide access to an appraiser or an inspector to do an unaccompanied inspection but should minimize contact with that person. Buyers should not be present for inspections.
Agents cannot attend a final walk-through.