I think a good way of thinking about this is food laws - i am happy to pay for enforcement of laws that make sure when i buy beef it is not, in fact, horse meat, rather than having to carry round a testing kit or rely on reputation/brand etc.
Occasionally some work might be required to check new technologies are applied in a constructive way, e.g. that a new bleach used to whiten bread is safe.
Oh yes, and also there is a power imbalance between the individual consumer and corporations/market forces. Think of regulatory bodies as a "consumers union". Would it be possible to organise efficiently without the force of government?