Free-spins on slot machines introduce a salient moment of potentially large wins that might influence people to either quit or continue a gambling session. Two theoretical models make different predictions about why people quit a gambling session. From a behaviourist perspective, people quit a session when they are either satiated or the lack of rewards lead to the extinction of behaviour. Alternatively, from a behavioural-finance perspective, people quit due to the disposition effect: a general finding whereby investors tend to sell shares or other assets when the price has increased, but keep assets that have dropped in value. From the behaviourist perspective, we predict that people experience free spins as a moment of intermittent reinforcement, which should encourage them to continue gambling longer. According to the disposition effect, however, the large win would trigger risk-aversion, signalling an opportunity to “cash out” and lock-in the gain. In the present study, 188 gamblers (72 female) were randomly allocated to one of three conditions: control, early free-spins and late free-spins, in an online EGM simulation (points only). Consistent with the disposition effect, participants who received early free-spins quit earlier, placing significantly fewer bets, than those in control condition. The study suggests that free-spins, rather than being reinforcing within session, may signal an opportunity to quit early. In the discussion, however, we speculate on whether future research could demonstrate that a perceived lack of free spins in a session may keep players engaged longer.