In a way, you are not facing one problem, but two.  You have the probable taxi scam on one hand, and you also have a communication problem too.  If you are not fluent in Mandarin, or if you are alone, how to defend yourself and your pocketbook ?
In my case, when I am in my city, I am aware of what the fares should be for most rides.  Besides, I know my way around enough to know when I am being given the longest route.  Since I do not speak enough Mandarin to have an argument, I telephone my GF, explain to her the situation, and ask her to tell the taxi driver that he is taking the longer route, and I am aware that the fare should be around 25 Rmb (for example), and that will be all the money he would get no matter what.  Then I made a point to either write down or take a photo of their taxi driver permit, which has the photo, name and driver's number on display inside the taxi, and that is enough to avoid further complications.

When I visit other cities, I do make a point to remember taxi fares.  Like from airport or train station to hotel, hotel to downtown, etc.  I ask also at hotel desk what the average taxi fare would be prior to taking a taxi ride.  I will not make an argument for a few yuan, but if the fare was to be 40 yuan, and I am charged 90, then I will refuse full payment and stick with paying 40.  Go to the taking photo of ID, etc, and if they call police I will stick to my stand, and pay them back by registering a complain with their local taxi board.
Maybe it is a bit easier for me to recognize in which direction I am being driven.  In daytime, you have the sun, at night the moon and above all, the stars will tell you.  As an ald practicing sailor, I do know always if I want to go North, South or which way.  If the taxi takes another direction, then I satrt paying more attention to whatever turns he is making to decide if I am into a probable scam or not.

ovimaps on nokia smart phones or if you can get your hands on an android phone from outside of china you can get google maps. also it is a great idea to plan everything out. use google maps.com to get directions even from your smartphone. when they see you have a map they are less likely to try and screw you. also at the very least know the direction of where you are supposed to go and look very closely at the taxi driver. if he is acting off it means he is trying to screw you.

You could go to upto a taxi driver and ask how much to a destination before you get in, you could then compare with another taxi to see if ok and if they dont know where it is dont get in.  I have been in 2 taxis last week where i ended up giving directions as they didnt know where it was once i was in  and i am a foreinger they should know.  Also if you are staying in a hotel ask the receptioist how long it will take to get there, depending in which city you are in you should know roughly how much a ten minute journey should cost.

Before you get to your destination city, hop on line and ask the expat community (for obvious trips - train stations, airports, etc).

Also, ONLY get a taxi from a real taxi rank... avoid the guys who walk up to you and ask if you want a ride. ALWAYS get their number (should be on the dashboard).