The exact wording under the VWP is:
"For the purpose of the Visa Waiver Program, "business" generally refers to business activities other than the performance of skilled or unskilled labor. Examples of activities that are allowed include:
- engaging in international commercial transactions, which do not involve gainful employment in the United States (such as a merchant who takes orders in the U.S. for goods manufactured abroad, or who travels to the U.S. to purchase American-made goods for export from the U.S.);
- negotiating contracts;
- consulting with business associates; and
- participating in scientific, educational, professional or business conventions, conferences, or seminars.
The performance of any skilled or unskilled labor - even if it is unpaid - is most always prohibited. This includes performing work in the U.S. as a trainer or consultant."
I frequently visit the US under VWP for meetings with my company's global management and have never had an issue. Clearly however anyone who states their profession as "consultant" is going to raise a flag.