Not all cabs have seatbelts, but if you are sitting in the back seat and your taxi does have them, then it is a good idea to put it on. This is especially true if your taxi is going to be traveling along local highways or in bad weather.
Do you suspect that the meter is rigged? In general a meter should only click over to the next cost unit every four or five blocks. If it is clicking over once a block then it is probably rigged to rip you off.
In terms of tipping it is customary to leave between 15% to 20% of the total fare as a tip. If you are not satisfied you do have the option of leaving no tip, but it is recommend that you leave a tip that is around 5 to 10% instead.