You're supposed to know when the price has changed, even if it hasn't. All rates quoted above are for one stop, from the street, and exact payment. Prices from further out in the Hotel Zone vary according to distance. Any additional services, such as giving you change or waiting while you get your laundry will be charged for at arbitrary prices that will vary with each driver and the phase of the moon. Ask before getting in.
Most hotels have the current sitio fares posted.
Street prices from their zones will be proportionately lower, but many drivers will charge gringos the sitio price anyway. On longer trips, such as to the airport or to Puerto Morelos to eat, negotiate the price in advance. A little bargaining is acceptable on longer trips. As a general rule, radio taxis charge higher rates and are more likely to have annoying drivers who yap incessantly on the CB and drive like maniacs. The best driver for a longer trip is usually middle-aged.