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As I claimed, it's a discussion not yes or no answer. Here are my two cents - I usually use the self-referral canonical to avoid and more duplicates, just like any other pages. I'll give you a quick example: Lets say you have this page: example.com/shoes?p=1 In case I use the other filters onsite (very common to eCommerce sites) it might look like this: example.com/shoes?p=1&type=nike&color=red To avoid this I use the self-referral canonical anyway.

Hi Shahar, Thanks for the question. As the other guys have said, it's hard to predict how the search engines will react to hidden content. In this case though, I highly doubt that this form would cause a penalty. You're not hiding this content with the intent of manipulation or anything like that and if a Googler were to look at this, they'd see that you're not to hide anything bad. I hope that helps! Paddy

Hi Kristina, Thanks for that, I really appreciate it. I'll follow Rand's tweet for additional insights.