In his book Word Of Mouth II,
Dave Balter talks about
an experiment described in the scientific paper
Effort Of Payment.
A research subject asked people
to help him move,
offering them different rewards.
People were least likely to help
when offered money.
Why?
Because money made the helpers
evaluate their assistance
as work for hire
rather than helping a friend.
In fact, people will make more of an effort
for no payment
than for a low cash amount.
Make cash rewards significant
or don’t offer them at all.