The 30 percent corporate tax dissuades companies that do business in American from locating themselves in America. Cutting this down to 9, would make it much more appealing for them to do so.
As for importation, 22 percent of every good (sometimes more) is consumed by taxes, irrespective of importation or no. These are all hidden taxes built into the price. All of these go away. So while the sales tax will increase the price by 9 percent, the actual price would come down. America would be closer to the actual world price of imported goods, which makes them a more attractive destination to sell.
Suddenly it may make sense for us to move our manufacturing out of the country, for example Taiwan. All the parts used now bypass the taxman and its origin is no longer the US bypassing other countries retaliatory import fees on US goods. Our product could then ship directly to customers from Taiwan never entering the US.
Sorry, that part of Cain's plan is stupid and will have consequences that are not good.