No matter what type of installation method your product comes equipped with, the issue of them not sticking can be one that comes to the forefront. Even though you may want to blame the manufacturer, with it sometimes being their fault due to the quality, the issue may reside in how you are attempting to apply the shade. Whenever you are dealing with adhesives, suction cups, or materials that are designed to naturally stick to certain surfaces, you need to ensure that the sticking surface is clean.
So, before you think about placing them on your windows, clean the window with an appropriate cleaner and then wipe it down to dry. If they still do not stick efficiently after this, it may be a quality control issue.