In the meantime, you can adjust the machine's brightness level manually. Check your service manual, some machines will allow a more permanent adjustment, giving you time to wait for a more convenient day to have the machine serviced. If it appears that toner is spraying onto the copies, check the waste toner bottle. More than likely it is full, causing the toner to spill out onto the sheets as they go past. If the bottle isn't overfull, then you have a serious problem and need to call for service.
Fax machines have their own set of rules.
If your incoming documents are fine, but you are getting complaints about sloppy looking outgoing faxes, then you need to look at what is called the scanner. The scanner will appear to you as a thin strip of glass with LEDs underneath. Simply take a soft cloth with some isopropyl alcohol on it, and wipe away the ink and white out that is stuck to the scanner. This will solve your problems. Most other problems concerning received document quality can be solved by replacing the cartridge.