Is it legal to buy items online and sell them?

I often go on ebay and buy iPod cases and cords for $99 and even clothes for a couple bucks from Asia. I had an idea but need to know if it's legal to do. For example if I buy 10 of one shirt for $3 each or like 50 iPhone cables for $30, would I be able to sell the shirts for say $10 each or the cables for $5 each here in North America?

Added (1). I meant to say cables and cases for 99 cents not dollars haha

You would need to check with the local laws where you live. For example, say you live in south Australia you google South Australian law re selling things on ebay

Well yes they are your property! Your local city may cite you for operating a business without a permit. Depends on where you sell them. On ebay, or Craigslist, or Amazon should be fine. At a flea market is usually fine too! Sell them as an item that you bought, and just want to get your money back for because you never used them, they were a gift. Never make it look like a business, unless you want to actually set yourself up as a small business, which is alot of red tape. You should be fine unless you are selling huge amounts of items, instead of a few bucks on the side.

If you start selling on a regular basis or above a certain amount, you may need a business license. Importing a lot of stuff could also hit something with customs. Ebay should have guides somewhere that explain various requirements and things to keep in mind.

I'd also point out that lots of people sell these cheap Asian items already, or people just sell them directly from Asia. You're probably going to have a hard time competing, and people are also going to expect you to back up items that fail. By the time you cover return shipping and whatever else may be involved, you're likely to negate your profits.