Agent's Role in Apartment-Showing Process

This is not correct. The tenant is only responsible for providing access to the unit, if it is provided for in the rental agreement (most NY ones will contain a clause). The landlord, however, must provide reasonable notice of a scheduled showing.

I've seen it every which way. I've seen tenants doing showings bc they've got some relation with the agent , landlords doing showings in a no-fee situation, and cousin Vinny from Queens just helping out. If OP is the tenant, and none of these situations apply, then the answer is to read your lease for details of access - when the unit can be shown, notice periods, and whether the tenant and their dog must vacate or just permit access.