India, Aug. 20 -- Zerodha co-founder and CEO Nithin Kamath has shared a candid post on social media, reflecting on how India's largest stock brokerage built its massive user base, without relying on advertising or paid referral incentives.

"When we started Zerodha, we didn't have the money to advertise, not that it would've worked," Kamath wrote. "So the only way we could grow was through word of mouth and customer referrals."

According to Kamath, the key to driving those referrals wasn't marketing spend, but rather building products and services "that customers would talk about."

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Zerodha introduced its referral program back in 201...