The BBC reported that Google will no longer allow ads for high cost services that say they will help consumers use the Electronic System for Travel Authorization ("ESTA") run by the U.S. Department of Homeland Security.  

Foreign travelers who want to visit the U.S. under the visa waiver program must apply for authorization through ESTA.  For individuals to apply, the cost is about $14.  However, when foreign travelers apply through private ESTA providers, they can be charged significantly more than that.  

Google's advertising policies prohibit, "Charging for products or services where the primary offering is available from a government or public source for free or at a lower price."  Google does allow, however, the advertising of these types of products or services with other things sold by the marketer, so long as the free or low cost item isn't the primary offering.  For example, a marketer can advertise a travel package that bundles travel with a visa application.