The RNG
Modern slot machines are computerized. So the odds are whatever they are programmed to be. The reels and lever are present for historical and entertainment reasons only. It is a Random Number Generator that chooses the reels positions. The machine's software includes a Random Number Generator.
Random numbers are constantly generated by the RNG at an extremely high rate. When a player presses the Play button the most recent random number determines the result. The result varies depending on exactly when the game is played. A fraction of a second earlier or later, and the result would be different.
It was noticed that the RNG does not actually generate random numbers. Most RNGs will repeat their number sequence. Poor programming is its reason. Pseudo RNGs with very long periods canbe built relatively easily. There is no computer that is able to complete a single period in the expected lifetime of the universe. Ronald Dale Harris, a former slot machine programmer, was the only one who had access to the pseudo RNG code and seed values. It was he who discovered equations for specific gambling games like Keno. Thanks to them the fact that the next set of selected numbers would be based on the previous games became known. However, this is impossible for most machines, because the RNG picks numbers even when the machine is not being played. So you can't find an exact place of a number in the sequence.

Payout Percentage
The percentage of winnings paid out of the money that is wagered by players is 82–98 per cent. This is known as the theoretical payout percentage. The minimum theoretical payout percentage varies among jurisdictions. It is typically established by law or regulation. There is a certain winning pattern nearly in every casino. It contains the information about the amounts they pay and the frequencies of these pay-outs. The selection of the slot machines winning patterns is chosen in such a way that it could yield a certain fraction of the money played to the house. The players get the rest of the money.
A slot machine's software is written and the theoretical payout percentage is set simultaneously. Physical swap of the software is needed for changing the payout percentage after a slot machine has been placed on the gaming floor. Being a time-consuming process it is done not very often. One can find a tamper-evident seal on the EPROM in certain jurisdictions. Only Gaming Control Board officials can change it. Other jurisdictions randomly audit slot machines to ensure that they contain only approved software.
The technology being developed by the Nevada Gaming Commission would allow the casino's slot manager to change the game, the odds, and the payouts remotely. The change cannot be done instantaneously, but only after the selected machine has been idle for at least four minutes. After making the change the machine is locked to new players for four minutes, it displays an on-screen message informing potential players that a change is being made.

Machines That Are Linked
Often machines are linked together in a way that allows a group of machines to offer a particularly large prize, or jackpot. If a player gets a specific combination of symbols the progressive jackpot from this group of machines is given to him. The amount paid for the progressive jackpot is usually far higher than any single slot machine could pay on its own.
Sometimes multiple machines form multiple casinos. In these cases the manufacturer owning these machines is responsible for paying the jackpot.

Near-miss Programming
The reel display of modern slot machines is under computer software's control. Combinations that are close to winning combinations can be displayed on the slot machine intentionally.
Such showing combinations that are similar to winning combinations more frequently than would occur randomly is called near-miss programming.
A related phenomenon is sometimes called near-miss. The chance of a winning combination appearing on a pay line is controlled by the winning percentages programmed into the slot machine. However, the combinations appearing above and below the pay line are all roughly equally randomly distributed. There are roughly equally randomly distributed combinations above and below the pay line. This occurs if abbreviated physical reels are used to display a win pattern based upon the RNG. In video slot machines, virtual reels are used and the symbols that appear around the winning line are usually an accurate depiction of how the reels were mathematically modeled.
The Nevada Gaming Commission investigated the issue of a near-miss above or below the pay line. They ruled that this was legal, so long as the near-miss above or below the pay line was not specially programmed. In other words, the near-miss must be just as likely to occur as any other combination. Winning combinations aren't supposed to be shown more frequently than other combinations above or below the pay line.
In Australia the usage of near-miss programming, where a near miss is inaccurately displayed is also illegal. Stop motion cameras are used by regulators for manufacturer's practices audit.

Fraud
Sometimes mechanical slot machines and their coin acceptors seem to belong to cheating devices and other scams.
Modern slot machines are controlled by EPROM computer chips and coin acceptors have become obsolete in favor of bill acceptors. It is difficult to defraud these machines because they their bill acceptors are designed with advanced anti-cheating and anti-counterfeiting measures. One of the recent attempts at defrauding slot machines is directing microwaves toward it to disrupt its proper functioning.

There are at least two types of slot players.
The first type is a persistent player.
This type of slots player is the one that believes the win is right around the corner. Just a second and the coins will be flying all over the casino!
The player will play until the machine pays out. He must have found a machine that haven’t paid for a long period of time or he has inserted to many coins and has got nothing. They believe that a big win is sure to happen right now. The rush is that if they leave after depositing so much money in the machine it will erupt and the payouts will be often and large. Maybe it can really work if you have already spent thousands of dollars and have got nothing back. The machine can’t but paying.
Many years ago in the case of the payout players touch the coins to check whether he coins were hot or cold. If the coins where hot then the slot machine had not paid out in a while and to the chaser this was good as the machine was do. But in reality any machine has numerous lights which heat the coins.
The chaser.
The player have won and being reinforced by the win gains trust in the slot machine. There is some kind of comfort and trust between the slot machine and the player.