For coffee shops, we recommend 9 stamps for the 10th coffee free. This is achievable in 2 weeks for daily customers, feels fair and generous, and "10th free" is easy to explain.
Try Double Stamp Days on your slowest days to boost traffic. "Double stamps every Tuesday!" or "Morning Happy Hour: Double stamps before 9am" work great.
Most coffee shops see a 20-35% increase in customer visit frequency within the first 3 months of launching a loyalty program.