Try Scanning a Different Document or Photo (9900F, 5000F, 8000F, 3000ex/3000F, 3200F, 4200F)

If the quality of your scanned image is poor, check the item you are scanning to make sure that it is in good condition.  If it is not in good condition, then you may already be getting the best quality possible.  You should try scanning an image that is of good quality for comparison. 

If scanning a different image results in better quality, then the scanner should be fine.  As for the scanned images of poor quality, you may try adjusting some of the options from the Settings tab of Advanced Mode such as 'Reduce Dust and Scratches', 'Grain correction', etc., and then rescan your image.