If you're buying off the Internet, then it's best to buy through things like PayPal which offer buyer protection on eBay and such. However if you're worried about getting scammed, then ask your parents if you can borrow their credit card, because false credit card transactions can be stopped by the bank, but debit cards offer little to no false transaction protection.
You could get in trouble if you buy something and it doesn't go through for a few days. Some companies are weird like that. So I know people who will look at their balance and figure that's what they have instead of remembering that they spent more money. So all you have to do is keep good records and balance your checkbook.
Then make sure you NEVER give out your card number to anywhere sketchy or anything. Only to secure websites.
If you keep track of what you spend and you're safe and smart about giving out the card number, you should be fine.
What the fuck is with you people?