Perhaps you should try some spelling variations:
firms transaction » firms transactional, from transaction, sales transaction
firms sanitation » rural sanitation, site sanitation, city sanitation
transaction cost » transaction costs, transactions costs
harold firms » held firms
head firms » held firms, lead firms, help firms

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: (( head firms sanitation (services. OR series.) ) OR ( harold firms transaction cost. ))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "(( head firms sanitation (services. OR series.) ) or ( harold firms transaction cost. ))~".
• Adding a wildcard symbol may retrieve word variants: (( head firms sanitation (services. OR series.) ) or ( harold firms transaction cost. ))*.