Many times I avoided a bad purchase just by reading a few careful comments. It is interesting to see how different people value different aspects of a product. Very thin fabric may be fine for summer but often looks cheap and becomes see through. Bad lenses can cause eye strain, reflections and headache when you wear them for hours.
If anyone is interested in real user experiences, I sometimes write short notes about the shops I test.
You can find one of the pages here:
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In the end it is all about finding what matches your own habits and lifestyle. When every picture has different colors or extreme filters, it is usually a bad sign. Comfort around the heel and toes is more important than super fancy design. Bad lenses can cause eye strain, reflections and headache when you wear them for hours. People who share height and weight information make it easier to choose the right size. Recently I have been testing several online eyewear shops to compare frames and lenses. Of course we all have different taste, but patterns still appear in long discussions. I also check if the store explains how to measure PD and frame size clearly.
Hope this helps someone.