Currently their is no method to guarantee "fair play" for virtual casinos.
Bricks and mortar (Las Vegas type) casinos have Gaming Commissions. Here is an example of the problem.
Difference between a land based slot machine and a virtual slot.
Land based slot can not change. The electronics,software and machine are physically present at casino. A gaming commissioner can test any machine at any casino at any time. This gives a "Chance" of discovering a casino tampering with an approved gaming device.
Virtual Casinos do not physically exists. At present their is no "True" regulation. The software providers have psuedo-regulatory organizations and gaming commissions. None of these psuedo-regulatory organizations do anonymous random testing of the virtual games they are said to regulate.
The United States can not be expected to let its citizens be defrauded by Entity's residing in a trading partners jurisdiction.

The United States has no responsibility for proving that "fair play" exists outside its jurisdiction. By definition a virtual casino game can not be tested physically. It is the responsibility of the virtual casino industry have "true" regulation. At present Antigua and Barbados have no requirements for random,anonymous and independent testing of their virtual casinos. Virtual casinos in their jurisdiction can defraud U.S. Citizens of billions of dollars annually.