You can't persuade people that observation and coaching can and will be a positive experience - a professional, motivating discussion not a judgement or evaluation - unless that's actually true. It needs to be sincere. Teachers need a chance to share their thinking and ideas, not just be told what the observer thought. Once people experience that, they begin to value and trust it. But if you're relentlessly in 'drop in and tell them' mode, things won't change. It's no wonder so many teachers resist these things - because they've been burned by the stream of 'feedback' launched at them by a string of people who didn't think it was worth asking them first.