There are 463 registered businesses from the tertiary sector in 2016 which are engaged in trade, transportation, finance and business service, and community, social and personal services. Majority of these establishments are wholesale and retail stores selling various kinds of merchandise including meat, fish and vegetable dealers. There are also service shops, eateries, bakeries, food processors, drugstores, and amusement centers and video shops. Buying stations are found along M. L. Quezon Street where copra, palay and abaca are traded. Agricultural supplies, automotive parts dealers, appliance dealers and gasoline/refilling stations are also thriving. Trading and business transaction in Irosin are concentrated mainly at the Central Business District (CBD) in the town center. The highlights of CBD are the Irosin Public Market, Municipal Hall, Public Auditorium and the line of commercial establishments where commodity trading stations, wholesale and retail variety stores, banks and service shops are found. Presently, a commercial strip is growing from the corner of J. P. Rizal and M. L. Quezon Streets stretching all the way to the Maharlika Highway.
The financial institutions in Irosin are the Land Bank of the Philippines, Rural Bank of Irosin, East-West Rural Bank, Camalig Bank, Card Bank and Rural Bank of Guinobatan. The Land Bank of the Philippines-Irosin Branch caters to a wide range of customers from local government units, cooperatives as well as commercial and industrial establishments from micro to large enterprises. The bank likewise accept savings, current and time deposits and foreign currency exchange particularly dollar and serves as a collecting agency of the Bureau of Internal Revenue (BIR), Social Security System (SSS) and Philippine Health Insurance. There are also many microfinancing institutions in Irosin namely ARDCI NGO Group, ASA Philippines Foundation, Equalshare Credit Corporation, First Consolidate Bank, First Inner Trade Credit Corporation as well as cooperatives offering financing services.
The increasing population in the rural barangays led to the setting up of barangays centers where public markets, chapel, health centers, barangay halls and multi-purpose pavements are normally clustered. Such centers are located in the barangays of Gabao, Batang, Monbon, Patag and Gulang-Gulang. Of the convergence areas Gabao is the most progressive.