  The European Union's General Data Protection Regulation (GDPR) requires
websites to ask for consent to the use of cookies for \emph{specific purposes}.
This enlarges the relevant design space for consent dialogs. Websites could try
to maximize click-through rates and positive consent decision, even at the risk
of users agreeing to more purposes than intended. We evaluate a practice
observed on popular websites by conducting an experiment with one control and
two treatment groups ($N=150$ university students in two countries). We
hypothesize that users' consent decision is influenced by (1) the number of
options, connecting to the theory of choice proliferation, and (2) the presence
of a highlighted default button (``select all''), connecting to theories of
social norms and deception in consumer research. The results show that
participants who see a default button accept cookies for more purposes than the
control group, while being less able to correctly recall their choice. After
being reminded of their choice, they regret it more often and perceive the
consent dialog as more deceptive than the control group. Whether users are
presented one or three purposes has no significant effect on their decisions
and perceptions. We discuss the results and outline policy implications.
