When you do any dealing with internet, you must ask questions. In case of cash for gold deals it is more important as gold is a very sensitive commodity that scammers are always eying for. As such, you need to take all the precautionary measures to avoid scams. There are enough reputed online pawnshops and buyers of jewelry to deal with.
One of the ways to find if the company you have found is a scam or not is to question them over the phone. You could ask for their location. Also you have the option to ask them their commissions and fees. Also it is good to know the way they do the shipments.
Ask for the price they offer for your jewelry. If they offer anything less than 80% of the spot price of gold, never try any transaction with the company. If you follow these precautions there is no reason for you to get caught to scammers.