It'd be interesting to know how Booking.com, a good example of these tactics, uses "scarcity" messages, as every time I try to book something on that website I always get messages like "only 2 left" and "5 people looking at this right now".
I think Booking.com was actually a client of Persuasion API; a competitor of Conversify (coincidentally all three Dutch companies.)
I think they actually ran this experiment only through their mailing list though but either way Booking.com was already using all these conversion tactics before though so at best they actually used this to occasionally turn off some of the less effective social proofs.
