Ensuring sustainable access to the data collected and produced in research processes is a critical concern for governments and research funding bodies in Europe and internationally. Research Performing Organisations (RPOs) such as universities and research institutes are key players in this endeavour. This requires data to be produced and managed according to the FAIR data stewardship principles, to be Findable, Accessible, Interoperable, and Reusable. Curating the data involves keeping it FAIR, and this requires services capable of applying the TRUST principles. These involve providing Transparency about data holdings, taking Responsibility for the data integrity, maintaining User focus to serve communities, ensuring Sustainability of services to preserve data, and utilizing Technology to fulfill these principles. To make this happen, RPOs can partner with Trustworthy Repositories to achieve a level of technical preparedness that will ensure long-term accessibility to publicly-funded data holdings. This guide aims to offer RPO staff help to identify an appropriate level of preparedness for their circumstances. ACME-FAIR is a 7-part guide developed in the FAIRsFAIR project, whose main purpose is to help managers of Research Data Management and related professional services to self-assess how they are enabling researchers, and the professional staff who support them, to put the FAIR data principles into practice (for short we refer to this as ���FAIR-enabling practice���). This part addresses the key issue of ensuring trustworthy curation.