There is a trick question that a cab driver will ask you as soon as your luggage is loaded and you are in the cab and he strikes up the conversation...
Is this your first trip to Vegas?
What he really means is Will you know it if I am screwing you?
There are a couple of simple things you can do to avoid all of this.
1) The first you need to know is ALL CABS that service McCarran Airport have the SAME METER RATE. The rate MUST be posted on the door or someplace you can see before you get into the cab. The meter starts at (Flag Drop) $3.30 PLUS an Airport FEE of $1.20 so actually you are going to pay $4.50 before you start. The rate per mile is $2.20 PLUS Traffic Delay time, usually about $36/hour = $18/half hour = $9/ 15 minutes = $3/5 minutes BUT this charge is only added when the cab is moving under 10 mph with most meters.
2) Go to a map program like Google Maps and find out how far your trip is. Say your trip is 4 miles: 4X2.20=8.80+4.50=13.30 PLUS Traffic Delay +-$3 or so... Your cab fare should be about $16+-
3) What I do is just tell the driver "Will $20 get us to Bally's?"
Works like a charm!