It was feared that the sex purchase act would lead to a change in market dominance, from street markets to indoor markets. Thus, we had to investigate the impact of the law on the activities in the indoor market.
Estimates of the size of the indoor market are considerably more uncertain than the estimates of size of the street market. This is due to the increasing rotation of the market. The prostitutes frequently travel across cities and countries and only stay at one place for a short term. Furthermore, it is common to have several advertisements connected to the same telephone number (in the sense of a call centre), to have more than one telephone number, and to have more than one advertisement on the same website.