If you are shopping online,

how do you determine whether the merchant is trustworthy?

Do you use a different method to determine trustworthiness when you walk into a store and need to use a credit card for a purchase?

Who is better positioned to regulate online transactions and handle irregularities or complaints consumer advocacy groups or the government?

You might need to do some research on the purposes and functions of consumer advocacy groups AND the method of filing a consumer complaint with a consumer protection office (government agency).