Tomás is a real estate agent in Madrid with 20 active apartments on DOMIVENDOMO. His monthly bill: $400 (20 × $20/listing).
Twelve sign up and become paying users. Tomás earns 12 × $20 = $240 in account credit. Next month his bill drops from $400 to $160. The month after, he refers eight more — his bill goes negative, building a balance.