There are many OER available under different licenses. It’s the same level of difficulty to recognize and legally use compatible materials

This is true that OER published under particular Creative Commons licence may not be compatible with each other but traditional copyright is not straightforward either and may lead to even more questions than compatibility of CC licences itself. The first

OER can led to using unverified materials by teachers and students

The level of assurance you can get from OER materials can be the same as with traditional materials: high when from institutionally reviewed process, lower when not reviewed or just found on the web. It depends on the country, but

Teachers need more time and work to adapt OER

Discussing teachers’ work on preparation and adoption of learning materials is a much more complex issue and depends on many factors. Changes to resource-based learning which are happening recently are a part of increased work time needed for teachers to

OER’s will damage publishing market

What damages the publishing market is not openness, it is the low adaptability to changes brought by new technologies. Open Educational Resources bring more competitiveness and disruption into educational publishing market but they are not damaging it. Instead OER bring