"There are many good, practical reasons for side-betting to exist and to thrive in the sometimes dark world of Macau’s VIP sector. Side-betting is in essence a private arrangement between junket agents and their customers, governing the size of the bets placed. Most commonly, it occurs in two basic forms, with essentially the same outcome.

The first is when the agent agrees with players that whatever the value of chips placed on the table, the real ante is multiplied by an agreed number. For example, if the customer placed a HK$1,000 bet and the agreed multiplier is 10, then the ‘real’ bet is HK$10,000.

The second common form of side-betting is when it’s agreed that the ‘real’ bet is denominated in a different currency to that of the actual chips placed. For example, the customer places a HK$1,000 chip on the table, but agrees with the junket operator that the bet is in reality denominated in US dollars, so the ‘real’ bet is US$1,000, which represents a multiplier of 7.8 times.

Such arrangements appear particularly convenient because the majority of junket customers in Macau hail from mainland China and do not—and in any case cannot—bring money with them to play, and instead rely on credit extended by junket agents. When a customer requests HK$1 million credit, the junket agent can merely request the casino provide HK$100,000 worth of chips, with the implicit understanding between the junket agent and customer that a ten times multiplier is in effect. Where side-betting involves a ten times multiplier, the result is that the government and casino licensee’s share of revenue is reduced to a tenth of what it should be. That means the government is getting only around 4% of the ‘real’ gross, rather than 40%, as tax."

Ref:https://www.asgam.com/index.php/2011/05/01/wheres-the-money/