Ask also if the broker ever uses non-online sources. Very often the information you need will not be in a database, and good information brokers will acknowledge that they can't always get what you need online. And some information is so deeply buried that the cost of pulling it up exceeds its value. An information broker is in business. That means it's going to cost you money to get the information you need.
Some brokers bill hourly, others bill on a project basis.
You may be asked for funds upfront or for payment upon receipt or on 30-day terms. Many information professionals have minimum fees. Ask about these practices, and ask for an estimate of costs. All of these are valid approaches to billing. However, you should ask these questions early, and be comfortable with the response.