Should I cancel accounts and give back refunds?
That depends. Why are you trying to cancel these accounts?
I'm trying to avoid getting scammed by the websites
That's really kind of you to look out for people like this, you are giving a good reputation to the company. It is not nice to be scammed, and if you didn't protect them like this countless people would lose so much money.
I don't know how much that is going to do to protect them.
Even if it not a lot, any protection can help out a little. It is so generous of you to want to help them out from being scammed.