Taxi companies in Shanghai are heavily regulated.  On the back of the plastic guard shield surrounding the driver, is written the local regulations in both Chinese and English.  They go something like:  the driver must always: greet the passenger, comply with all requests to turn on/off the radio or air conditioning/heating, not spit or throw things from the taxi, must always provide a receipt, etc. etc.  All taxis - without exception - must be metered, and all meters must be capable of printing official receipts.  To ask for a receipt after the journey (assuming it is not automatically offered to you by the driver), simply say "fah piaow".  If the driver doesn't give you one or breaks any of these regs, you are entitled to leave the taxi without paying and can report him to the authorities.

By far the best taxi company in Shanghai is Dazhong Taxis.  They are the light blue/aqua coloured ones, with the number 96822 in a splash on the side.  96822 is their phone number, and they have an English-speaking booking service which to the writer's best knowledge is unique among taxi companies in Shanghai.  Receipts are always offered automatically by the driver and the drivers always know where they are going, which in a megalopolis like Shanghai is impressive.

One taxi company to be avoided is the company with maroon liveried taxis.  It has been reported that they attempt to con passengers by saying "fixed price, RMB150" or "meter broken, fixed price".   RMB150 would normally get you over an hour's taxi ride.  The journeys these taxis wanted to charge a fixed price for were ones which should cost around RMB25.  If this happens to you simply tell the driver to stop and just get out, taking a note of his driver licence number (which should be displayed on a card on the dashboard), failing which a note of his vehicle registration number.  If their meter is truly broken then they are not allowed to pick up passengers.