This document discusses experiences with evaluating open educational resources (OER) in the Netherlands. It describes Wikiwijs, a national OER platform launched in 2009 to develop and share OER. Wikiwijs now hosts over 1.6 million OER building blocks and 48,000 lessons. The document then discusses using quality marks assigned by peer review or organizations to help teachers identify high-quality OER. It notes that teachers find quality marks more reliable than ratings, and that transparency is important to build trust. Finally, it shares that teachers report the presence of a quality mark is more important than which specific mark is used.