In every city that has taxicabs in service, there are certain rules for how customers tip for service - or whether they even tip at all. As everyone in Las Vegas seems to expect to receive tips, it's no wonder that the cab drivers are always trying to get you to tip them, and some of them will do almost anything to try and get a better tip out of you.
I personally have my own set of rules for tipping taxi drivers in Vegas, and not everyone will agree with me on my method or reasoning for determining a tip. They shouldn't, either; a tip is a thank you for good service, and it is obviously going to vary from person to person depending on what good service means to them. So, use this as a guide or ignore it altogether, but I try to be fair and not go broke at the same time.
I start a kind of calculator in my head when I first see my cab pulling up to the curb at the airport. By the time I get to my hotel, I have been adding or deducting depending on how things went and will pay the cab driver accordingly.
Arriving in Vegas - If my cab driver places my bags in the car at the airport and takes them out at the hotel, they are definitely the recipient of an extra 50 cents at this point. Usually the skycap will load the bags into the cab at the airport, or I may even do it myself. My tip counter starts here when I see how the cab driver does when I'm getting into the cab.
Traveling to the hotel - On the way to the hotel, I have several things I look for:
Is the cab driver trying to kill me by dodging in and out of traffic repeatedly?
Are they cursing and/or sharing their extreme religious (or racist) beliefs with me?
Are they blasting me out of the car with their loud music, smoking, or too much air conditioning (or none at all)?
Did they follow my instructions for getting to my destination (if I asked)?
If they're nice and they have avoided these issues, a $1-$2 tip is added into the total in my head.
Arriving at the hotel - If the cab driver has been polite and provided what I feel is good service up to this point, I just wait to see how they do when they take the bags out of the cab. I've had a couple who haven't even gotten out of the cab to take the bags out for me, and it's usually because they've been pretty surly on the trip to the hotel and they know they're not getting much of a tip, so they no longer make an effort to even be civil. If they get out and take the bags out for me, I mentally add another 50 cents in.
For a good ride where the cabbie was civil and helpful, the total tip is now $2 - $3 on top of the fare, depending on how happy I am with the ride. If I were carrying an extra-heavy bag or got some good info on a restaurant or something from the driver, it'd be $3 - $4 on top of the fare, but that's me.
If the ride was crappy, the driver unpleasant, and my life or health was in danger in any way, I simply round up the fare to the next dollar, say "thank you", and take my bags. I may get dirty looks or get cussed out, but I'm not tipping someone who thinks they are automatically deserving of any tip. Sorry, that's just me.
Returning to the airport - Just reverse the order above. Same rules apply.
Driving anywhere in Las Vegas - I generally walk anywhere in Las Vegas that I wish to go, or I take the monorail from one end of the Strip to the other, but if I'm traveling with my mom or someone else who isn't used to all the walking in Las Vegas, I might take a cab. In this instance, I follow the "traveling to the hotel" set of questions to make sure I wasn't almost killed, I didn't suffer damage to my hearing or my lungs, and when I asked the driver to take a certain route he actually followed my directions. If the report is good in all those instances, I will add $2 - $3 to the top of the fare, depending on the length of the trip.
I have had a couple of occasions where I have given the driver less than the fare, though, and I think it's something that should be addressed here.
On a trip from the airport to the hotel, a cab driver took the tunnel route (along I-15) instead of the route along Koval Road that I had asked him to at the airport, and I called him on it. After much arguing - and a $23 fare from McCarran Airport to Harrah's - he told me to pay what I thought the trip fare should have been, so I gave him $14. It was the average amount of my previous fares on the route that I have traveled many times. He didn't argue with me, but he wasn't pleased, either.
On another occasion, my mother and I took a taxi from Wynn to Luxor because of her inability to walk the distance. The taxi driver went across Las Vegas Boulevard to I-15 and took the highway (with rush hour traffic) to the backside of Luxor, then wouldn't drive under the portico to queue up with the taxi line like he was supposed to do. I advised him of the issues I had as soon as he crossed over to the highway, and he pretended not to hear me during the entire trip. The fare would've been $16 for that trip, and I advised him I wouldn't pay it and had a good mind to report him. He, too, advised me to pay what I thought the trip was worth, and I gave him $7 (even though I should have given him $6 or less), and walked away. He yelled a few obscenities at my back, but I stood my ground and advised the valet attendant to watch out for him. I' can't be mistaken for a shrinking violet, can I?
If you feel that the cab driver has "long-hauled" you, you should speak up and tell them so. There are strict rules that cab drivers must follow when transporting passengers around Las Vegas, and they are aware that their passengers have a right to report them to the Taxicab Authority if they feel they are cheated. Taxi drivers do not want to be given a warning by the TA, because they could very well lose their job over a couple of bad reports.
In the end, use your instincts and tip what you think a taxicab driver deserves, not what they expect. The two things are not always the same.