The FDA does regulate herbals, but to a lesser extent. The FTC controls the advertising claims since these products are technically foods. We don't want to get to the point where cereals that are high in fiber, like All Bran, get regulated by the FDA.
There are several non-governmental agencies that evaluate herbal medications for having the correct herb, potency, bioavailability and consistency in batches. The herbals that pass tests will have a "seal of approval" from that agency. I would steer customers towards those products, if they plan to use an herbal.