Assuming a merchant accept Bitcoin,
You as a shopper, place an order, and that merchant did not deliver, or sent to the wrong address, or sent a fake product.
You can not reverse the payment, you can get your bitcoins back, and the only thing you can do it leave a negative feedback.
Of course, there are many other scenarios, like phishing websites, fake websites, selective scams, and so on
What are your thoughts and ideas to prevent these scams.
First of all, bitcoin is not paypal who's capable of doing what you mentioned. The system of bitcoin is very much transparent to us and we know it's limitation so under the situation, it should be the transacting parties initiative to transact safely. Bitcoin was not created solely for online shopping, it's just a currency that can be use for online transaction and it has nothing to do with the safety of both party to make a successful transaction.