The quality of your photos will reflect (for better or worse) the quality of your products, at least in the perception of your consumers.
If you have great products but mediocre photos of them, people looking at these images on your site are going to think that your products are as poor quality as your photos.On the flip side, professional quality photographs will improve the public perception of your products greatly.
Product photographers know all the tricks of the trade (lighting, placement, etc.) to make sure that your photos look the best that they possibly can.