The assurance contract mechanism is often used to crowdfund public goods. This mechanism has weak implementation properties that can lead to miscoordination and failure to produce socially valuable projects. To encourage early contributions, we extend the assurance contract mechanism with refund bonuses rewarded only to early contributors in the event of fundraising failure. The experimental results show that our proposed solution is very effective in inducing early cooperation and increasing fundraising success. Limiting refund bonuses to early contributors works as well as offering refund bonuses to all potential contributors, while also reducing the amount of bonuses paid. We find that refund bonuses can increase the rate of campaign success by 50% or more. Moreover, we find that even taking into account campaign failures, refund bonuses can be financially self-sustainable suggesting the real world value of extending assurance contracts with refund bonuses.

担保合约机制常用于众筹公共产品。这种机制具有薄弱的实施特性，可能导致协调不当和无法产生具有社会价值的项目。为了鼓励早期贡献，我们扩展了保证合同机制，在筹款失败时仅奖励早期贡献者的退款奖金。实验结果表明，我们提出的解决方案在诱导早期合作和提高筹款成功率方面非常有效。将退款奖金限制为早期贡献者的工作以及向所有潜在贡献者提供退款奖金，同时还减少了支付的奖金金额。我们发现退款奖金可以将活动成功率提高 50% 或更多。此外，我们发现即使考虑到竞选失败，