I wouldn't say they're all bad. It really depends on your bargaining skills but I usually pay around the same price as a regular taxi fair. Sure, when they see a foreigner they'll try their luck to get a few extra bucks outta you, but usually I find they're really eager for business, so if you do the whole walking away to find a more reasonable fair thing, then they usually give in and give you a lower rate.

Agreed. I live in a far off place in Shenzhen (yantian port) where no normal taxis will ever go. The few that I managed to drag over there only accepted because they hadn't realized how far and lost it was.

With black cabs just make sure you negotiate things properly at the beginning, and in the end you can settle for something very close to what the price might have been with a normal cab.

And as you said, not all normal cabs are 'legit' in their dealings. One of the taxis I took put a cloth over the meter when I wasn't looking, and when I arrived asked for 3 times the amount. When I asked him why the meter didn't read anything, he said he thought I didn't want a fapiao.

Not all. Some are good in the local communities. But if you are at a touristy area, they won't give you a normal price because some other person will probably pay their ridiculous price.

If using a black cab you need to know the price of the real cab to that place, if you know it should be 13rmb you tell them 13rmb for me they almost always if reluctantly accept...i have never tried to negotiate them to a better deal, if i dont know the price i get a normal taxi

i think you should take the cab with mile meter , and ask for receipt everytime.

In response to you direct question about whether black cabs always cheat?
Yes!
...and blue...and white......and.........