Measure success on three levels. Level 1: direct feedback. Send a short survey within 48 hours after return. Ask about experience, highlights and points for improvement.
Level 2: behavioural change. After 3 months, look at performance indicators like revenue, productivity or client satisfaction. Level 3: retention and motivation. Track turnover and staff satisfaction over a longer period.
The best incentive programmes show a measurable rise across all three levels.