Heading out for holiday cheer, tonight we go behind the bar. That drink you ordered, what's in your glass? Only the bartender knows for sure. Amy robach with the bartenders serving up confessions... See More
Heading out for holiday cheer, tonight we go behind the bar. That drink you ordered, what's in your glass? Only the bartender knows for sure. Amy robach with the bartenders serving up confessions tonight. Reporter: Frighy nit. Step into a bar almost anywhere wildness in bar ..And you'll find people looking to unwind . Bust loose...And get their drink on. But someone has to run the party. And that someone .Is the master of mixology the bartender. Because ultimately you're in control. Yes. Reporter: You have got the alcohol. Exactly. Reporter: And that's what they want! The customer is king in the service business. But you know it's not absolute. Whether it's absolute, heineken, or jack daniels, ben molina has poured it all. I'm thinking we're doing something fun, something exciting with whiskey. There you are customer. Thank you sir. Thank you, enjoy!! And the bartender and co-owner of cinco in los angeles. Poured it all out to us. Revealing all the little ways barkeeps can mess with customers they don't like. How do you deal with rude drunk people? Um there are steps you can take. Reporter: Steps bartenders rather you don't know, such as. The silent treatment. An obnoxious customer might simply get ignored. Reporter: Deliberately not get their next drink? Oh yeah absolutely. Reporter: You have that power. You can make em wait. Yes! Reporter: The disappearing liquor treatment the next drink might come minus the alcohol. It can get nasty when people want their drinks. Reporter: And step three? How about the visine treatment! A few drops and an unscrupulous bartender can send you running to the bathroom or home! Sometimes the visine is a better alternative than a fight! Reporter: Jon taffer is the host of the spike tv show bar rescue. Every week he finds another bar with another dirty secret. I got your friggen game and i know exactly what you're up to! Reporter: And here's his sad but true confession. Some bars mess with everybody, not just the rowdy drunk. How often have you found bars ripping off the customer? You know all too often. Reporter: He met with us at new york's marquee club to demonstrate how easy it is for a bartender to cheat you. By demonstrating three cocktail cons. The short pour. I'm going to charge you for a full drink, and give you about half a drink. Reporter: And I'm not going to know? You won't know it. I'm going to take an ounce of scotch and put it in a shot glass. I'm going to take about half an ounce and put it in that shot glass. Reporter: It's less until you add this. Pounding crushed ice crushed ice. The key to the con! One of the things you look out for in a bar is crushed ice in the bin. Reporter: Who knew? Watch what happens. Look at the difference! Reporter: It looks almost the same that even looks a little more! Big ripoff! Reporter: So you can pour a lot less and make it look the same? You got it! If I top this with cola, look how little it takes. So this one I ripped you off with half as much liquor and you think it's a better drink! Reporter: Wow! This is what we call the long pour! What you think is the long pour. I give you a look. How are you? That real special look. Reporter: Little twinkle in your eye! Im going to take care of you right. I put that bottle up. Reporter: Wow. Long pour. You think you got a lot. You didn't! When you lift that arm. You create the illusion of quantity. It's all illusion. You felt special. And I'm ripping you off! And last but not least. The sneaky pour. This is one of the sneakiest things a bartender could ever do. So you're going to see me pour a real lot 3, 4, 5, 6, 7. Now that's as much time as 2 and a half ounces of liquor would be. Reporter: Fills the drink with soda and plops in a straw. A nice looking drink, but he's ripped you off, how? Every liquor bottle has an air hole. When I cover that air hole with my finger, the fluid stops coming out. Here is the normal pour, normal. With my finger. Reporter: He pours a week drink but you're convinced it's strong. Because of this. And when I take that straw out and I put it in your drink, what's the first sip you're going to get out of that straw? Reporter: This is a good strong drink. Straight vodka. Reporter: And after that you forget that the drink is kind of weak? Forget it? You're saying jon, great drink! Great drink! And you're throwing the tips at me! But taffer says bars don't even need to know this sleight of hand to con you. Sometimes people are losing so much money, and they get desperate. Reporter: They'll do whatever it takes. They do. Reporter: For instance, the oldest trick in the bartending book, pouring cheap stuff into empty bottles of top shelf liquor. Or simply watering down the booze. Easy to do. Very hard to prove. I don't think that tastes like tanqueray! That tastes cheap. Reporter: Can you really taste the difference if it's mixed in something else? I would say probably 90% of the people -- no. Reporter: Have no idea what alcohol they're actually drinking. They wouldn't know the difference between a well vodka and a grey goose or you know? Reporter: Back in los angeles, ben's helping us put that to the test we bring in two panels of four volueers. We're going to have a little fun here. Reporter: Ben mixes three vodka and cranberry drinks for each of them. One with grey goose. The other two using a brand no one knows, nikolai! This is a bottom of the barrel vodka. Reporter: The drinks all look the same. Will they taste different? Go with your instincts and pick which one you think is grey goose all right well let the games begin. Yeah, they're all great! I'm really battling between two of them. The grey goose is in glass number one for every person. On the count of three, one, two, three, reveal! Reporter: Both times it's the same. Three out of four drinkers get it wrong! They would have been easy victims. Yeah that is kind of unsettling! Yeah I would definitely feel ripped off. It kind of makes you think why is this alcohol so much more expensive if you can't tell the difference between the two? Reporter: That's what todd tarczynski wants to know too. He was a regular customer at this tgi friday's in new jersey, his usual drink: What else? Grey goose with cranberry juice. I'm not usually watching the bartender. Simply because I never thought i had to. Reporter: But then he heard some wild news. Something called operation swill. More information is coming out about operation swill. Cheaper liquor disguised in top shelf bottles. Reporter: The new jersey attorney general busted 29 bars all around the state, including that tgi friday's. Accusing them of not just serving their customers the wrong booze but even rubbing alcohol! Tgi friday's settled, but admitted no wrong doing. I was shocked, I was very angry and shocked. Reporter: Todd was so upset. He sued. A class action which his lawyer says could be just the tip of the iceberg. It's the epitome of desperation. It's stupidity. Reporter: Bottom line. Want a stress free trip to the bar? Reporter: What is your ultimate advice for people when they walk up to a bar? Be educated. Understand what a pour looks like, how much alcohol you should be getting and the most important way you guarantee good service is leave when you don't get it. A 20/20 contactsed those restaurants sued in new jersey who told us there was never evidence of a widespread problem, and that the true facts will emerge in court. In the meantime, tonight, what about you? Have you ever wondered what's really in the glass? Ever think you've been fooled? Tweet us. And next right here you have to
This transcript has been automatically generated and may not be 100% accurate.