Referral incentive design — pick the currency

Why cash referrals for ordinary users don't produce growth

1. Incentives cannot conjure distribution. An ordinary user's circle holds one or two people in-market at any moment; however motivated, he cannot reach more buyers. Commissions make people with audiences work harder; they give people without audiences nothing to work with. (LingQ has offered 20% lifetime for years; nobody counts it among their growth causes.)
2. Pricing the favor destroys it. Recommending something to a friend is a favor — social currency, priceless. Attach cash and the same act is re-priced as low-wage selling. The classic evidence: the Israeli daycare that fined late parents and got MORE lateness; paid blood donation lowering willingness. The kill is double: the sharer pre-cringes and shares less; the receiver hears a salesman and discounts.
3. It selects the wrong responders: the people a cash link motivates are, by definition, people posting links for money — spam, self-referral fraud, coupon arbitrage.

Where incentivized referral DID drive growth — and each case's condition

• PayPal (cash, both sides): the product IS money, and claiming the reward required performing the product's core action;
• Dropbox (storage, both sides): reward in product currency, universal need, sharing built into use (~35% of signups at peak);
• Uber and the delivery wars (ride credits): really subsidized paid acquisition wearing a trust skin — died when subsidies did;
• Fintech signup bonuses: cash is the category's native language;
• 拼多多砍一刀: the frame inverted to favor-ASKING ("help me cut"), which Chinese social norms accommodate — selling re-disguised as a favor;
• Creator affiliate programs: the creator-audience relation is already openly commercial; cash changes nothing;
• Course-reselling waves and MLM: the limit case — they grow by forcibly re-denominating friendships into commercial relations; the burned relationships are the cost of goods.

The two general properties

1. The reward's currency must be of the same family as the relationship's currency. Gift-currencies (product credit, mutual benefit, help-me framing) pay friend-relations; cash pays only money-categories and openly commercial relations. A visible cash incentive re-denominates the act — and re-denominating is counterfeiting.
2. Good rewards are closed-loop: claiming is using. PayPal's payout required opening the account; Dropbox's space deepens lock-in; ride credits are the next ride. Rewards spendable only inside the product flow back as activation and retention; cash is pure leakage.

One line: referral design is currency selection — closed-loop inward, family-matched outward; cash is legal tender only where money is the topic or the relationship is already commerce.