Each search term put into a search engine produces a separate set of
results. Correspondingly, each of the sets of ads displayed alongside
the results is priced using a separate auction. We investigate how bids
for these context-based ads depends on the difficulty of making a match.
This contrasts with the existing literature that focuses on the effect
of match quality. We examine advertising prices paid by lawyers for 139
Google search terms in 195 locations. Other things being equal, the
fewer searches there are on a term, the higher the price. To identify a
causal relationship between match-difficulty and prices paid, we exploit
a natural experiment in 'ambulance-chaser' regulations across states.
When lawyers cannot contact a client by mail and matching becomes more
difficult, the relative price per ad click is $0.93 higher. We check the
robustness of this result by performing a falsification test using a
different ambulance-chaser regulation. Our results suggest that prices
are higher for context-based ads when the difficulty of both online and
off-line matching increases. This highlights that a major reason why
search advertising is profitable is because its use of context can
monetize the 'long tail' by reducing friction in the matching process