How can I avoid being overcharged when taking a cab?

Contrary to @Ginamin's answer, my advice, based on traveling in Mexico, as well as practically everything I've ever read on the subject, is to never use a metered taxi and always agree to a price up front.

The best prices are usually had when you pay at a kiosk, such as found at a bus station or airport.

Case in point: Yesterday I arrived in Morelia, Mexico, and took a taxi from the bus station to down town. I paid at the Kiosk. Cost: $35 pesos. Today when I returned to the bus station, I was lazy, and took a metered taxi. $70 pesos!!!

I've also been ripped-off by a metered taxi once in Tijuana, where the taxi driver kept the meter running while he filled up at the gas station!!!

Taxi meters can also be tampered with to run fast. Some are distance-based, some are time-based. Taxi drivers with time-based meters may drive extra slow. Taxi drivers with distance-based meters may take longer routes.

There are just too many ways to rig a taxi meter, unless you're in a jurisdiction where you trust the local government to enforce fair metering practices. So my advice is to never use a metered taxi, unless you're in such a place.

The book Travel Advisory, which I recently read, also suggests to always take only official taxis, and always agree to a price before entering the taxi. Never use a metered taxi.

In summary:

• Always know a fair price before you look for a taxi. Ask a friend, or ask a receptionist at your hotel or at the airport what a fair price is to your destination. If you can't do this, ask multiple taxi drivers before accepting a ride.

• Always agree to a price before getting into the taxi.

• Never trust a taxi meter. It can be rigged.

• Worse, don't trust an un-metered taxi when you haven't agreed to a price first.

• When possible, arrange your taxi travel through an official taxi kiosk (usually available at airports or bus stations, and perhaps some hotels)

• Ask the locals for any nuances in taxi travel where you'll be staying.

Depends on the country. Sometimes it's better to use meter, sometimes not.

Here are my tips:

• Ask lobby/local how much they think your ride should cost. If you want, you can take a cab without meter now based on this price.

• Do NOT take any taxi that is waiting outside of tourist hotspots/hotels. In many countries, these guys are the scamming drivers waiting for tourists to walk out. In some countries, they will even refuse to give rides to locals as they wait for gullible tourists. Just walk away as far as you can and hail a passing cab down the street.

During my trip to Costa Rica, we were advised to only take red taxis, as they are metered and regulated. But even when we got in the "right" cab, the driver didn't use the meter anyway, and so we had to negotiate the fare.

Despite our precautions, the drivers managed to pull a few tricks ("15 Dollars? No, 15,000 Colones!"), and over the course of the 4-day trip, we still managed to overpay by about $20-25 across all our taxi trips. Ah well.

From my trip to CR, here's what I learned:

• Only use official taxis displaying the correct designation/emblem/sticker/etc.
• Negotiate your fare with the driver before you get into the cab.
• Make sure both the amount and the currency are agreed upon.
• If there is a language barrier, try to learn the language basics before you go and/or bring a friend who is fluent.

From experience in India, many popular tourist routes are prepaid. The amount is decided by a regulatory authority such as the government or transport commission. For instance, the drive from the airport to destination X will cost only a Y amount of rupees. This ensures that drivers do not (in their own interest) meander their way to your destination in an attempt to drive up meter charges. The prepaid charge is usually paid ahead of time at a kiosk, which then issues a voucher to be given to the driver.

For more custom travel needs, an option is to negotiate a flat daily rate based on duration (and not distance traveled). Again, there are standard rates for this hire in India.

Finally: If you do realise that you are actually getting ripped off (e.g. the driver is asking for more than was agreed, you realise the meter is totally rigged), remember that the money is in your hand.

You can just get out of the taxi, and you should do so before paying. That way, you are in control of what you pay. Note that this won't work if your luggage is in the back.

Depends on the country.

Generally, in a place you're visiting for the first time and where scams are frequent, it's better to agree on the fare upfront. This way you will pay more than the ideal metered fare, but you limit surprises and scams.

If you know your way around already or the place is generally civilized and safe (e.g. Western Europe, Japan or Thailand), metered fares tend to be cheaper.

Knowing what the fare is supposed to be upfront helps in both cases, but is especially important with no meter. Looking at a map helps, and hotel front desk might help if they aren't in the business of hawking their own cabbies (in return for a commission).

It's good to know what the official or reputable taxi companies are (if they exist), and how to recognize their cars.

If you're going without meter, always clearly agree the amount and currency up front, and perhaps even write it down. If you have many pieces of luggage, and especially if you place it in the trunk, your bargaining power in case of a conflict is significantly reduced. Have small bills available (cabbies often pretend to have no change), and count your currency carefully when paying (some cabbies switch similar-looking bills).

In addition to the answers specifically about taxis, you may want to do some research on alternate taxi-like transportation: Uber, Le Cab and similar.