my 2 cents: I don’t think there is a ‘canned’ definition for “bonus abuse” but rather several different ways of describing it.
Since the word is used by casinos, I’m approaching it from their perspective: a bonus is issued to compensate a player before, during or after a deposit; the bonus is supposed to give that player more play time and afford him a chance to also win.
The bonus has terms and conditions attached, so that in 99% of the cases, the casino feel legitimately protected from having issued a bonus…
Those T&Cs (the “wagering requirements”) obligate the bonus to be ‘turned over’ a certain number of times, so the casino can at least break even on the cost of that bonus – in other words, the bonus needs to be exposed to a certain amount of ‘usage’ so that there is ample chance for it to be lost (but hopefully not such an extreme amount of usage, that the player himself feels abused)…
Now, what is the “bonus abuse”? If we assume that the bonuses are issued to standard ‘gamblers’ – people seeking entertainment, and hope, through chance and skill to win – the assumption is, they will gamble in a normative way: if they win a round, they will react accordingly, if they lose a round, they will react accordingly (eg. usually conservatively).
One kind of bonus abuse works against that above proposition: a player places his bets regardless of the outcomes of his rounds because he’s playing against a known statistical outcome. For example on BJ, he should have a near 50-50 chance of winning (or losing): he places his bets in a flat or even increasing pattern regardless of how the round ends. He may lose 6 times in a row, but continue flat betting – or more logically, doubling his bet – so that when he wins, he at least recuperates the losses from the previous rounds.
The lack of randomness in his game play raises flags at the casino; and if he is disciplined as well, he knows when to stop – when his session ends with him in the green, or at worst, close to zero, but almost never at a loss. It is that robotic, un-random behavior that can lead casinos to feel that the bonus is being “abused”.
There are other styles, such as making initial huge bets, to rack up a quick large balance (followed by very conservative game play, to husband the winnings).
When bonuses are cashable, bonus seekers tend to wager very conservatively; when bonuses are sticky, they go all-out and make very risky big stakes.
Fundamentally, the casinos are looking for ‘randomness’ and normative behavior in the betting patterns.
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Ironically, many gamblers know all this and don’t even use bonuses anymore – they do the same thing with their own money. The only recourse for casinos is to limit the players’ bet limits, to reduce the risk they pose.
…but psychologically bonuses still give punters a feeling of ‘wealth’, that they can afford to take a risk because there is ‘extra’ money in their account. As a result many players still prefer to receive bonuses instead of declining them…