There are three main causes of blurry images, out of focus subject, camera shake and the image captured at too low a resolution, sometimes all of these factors are the reason why your product images are blurry.
Out of focus images are by far the biggest problem with most of the product images seen on the internet, and all it takes to get good focus is a little bit of time getting to know your camera, learning to focus your camera is going to be time well spent. Using auto focus on your camera is fine, but it is important to understand how your camera's auto focus works and to know when to use your camera's macro focus setting is essential to taking good product shots.
Another extremely common cause of blurry images is camera shake or motion blur. Using a tripod along with the camera's self timer or a remote will eliminate motion blur in most cases. When taking close up photos of products in macro mode slightest movements of the product itself can cause motion blur so ensure you place your both your tripod and product on sturdy surfaces.
Although not as common a cause of blurry images as the other two, shooting the image at too low a resolution can result in a blurry image. You don't have to buy an expensive 14+ mega pixel camera, in fact most cameras on the market these days are sufficient to take your product shots. Camera phones while claiming high pixel resolutions are not good enough for your product photography.
It's necessary to shoot an image at a higher resolution than you intend use because a lot of the detail will be lost as the image is processed. Most product photographs need to be cropped, adjusted and resized, all of these cause loss of detail, just by saving your pictures as jpegs will cause loss of detail.