The Secret to Effective Fundraising Premiums

From the research I've seen, premiums can work to boost giving in the short term but also create some problems long term, especially if the premiums are positioned as a quid pro quo for a gift and have limited resonance with the cause. So what approach might be better? Mercy Corps chose to surprise donors with a gift tightly aligned with its cause, AFTER the donors gave. It was rooted in social, not market norms. The gift delighted donors without crowding out their emotional connection to Mercy Corps. It's an example of excellent cultivation.