Government Customer Service Accountability and Improvement Act of 2018 This bill requires the Office of Management and Budget (OMB) to select certain agencies, including at a minimum the Department of Veterans Affairs, the Office of Personnel Management, and the Internal Revenue Service, to develop customer experience standards and performance plans for such agencies. The senior accountable official for customer experience for each agency shall develop customer experience standards and performance plans, subject to approval by the agency and the OMB. The standards and performance plans shall be: (1) based on customer and market research that identifies the aspects of service delivery that are most important to citizens, and (2) collected through both qualitative and quantitative research methods that incorporate voluntary feedback from citizens. The approved standards and performance plans shall be included in the agency performance plans. The OMB shall establish the Service Improvement and Accountability Unit Pilot Program to provide assistance to an agency that does not meet applicable customer experience standards.