Until they realize it's just spam. Or they already know it and simply ignore such messages (e.g. LinkedIn recommendations, automatic invitations from random websites parsing your contact list...).
One rare instance where this seems to work (at least partially) is when both sender and receiver share some benefit from the advertisement, e.g. as when mobile phone operators offer discounts for inviting new users, both to the current user and to the newly invited one. So, if your coupon might get me some future discount should I go to that restaurant, then yes, maybe I'd consider it...
Until they realize it's just spam. Or they already know it and simply ignore such messages (e.g. LinkedIn recommendations, automatic invitations from random websites parsing your contact list...).
One rare instance where this seems to work (at least partially) is when both sender and receiver share some benefit from the advertisement, e.g. as when mobile phone operators offer discounts for inviting new users, both to the current user and to the newly invited one. So, if your coupon might get me some future discount should I go to that restaurant, then yes, maybe I'd consider it...