No meters....................the vast majority of taxi's have a laminated rate card either hanging from the rear view mirror or attached to the back of the front seat.
Yes, even though they are supposed to charge the "posted" rates, some drivers can be a little creative with what they charge. On your first ride in a taxi ask to see the rate card, make a mental note of the rates for places you will be going to. Ask the driver "how many peso's" before you get in, if he hits you with an out of line price, take the next taxi!
Most are Nissan Sentra's and are generally in good and newer condition...........tipping is optional and the amount is up to you. Remember a Peso is worth about 8 Cents.