Comment by CPLX

> it's an incentive to put it back in its place for people who were already not planning on stealing one.

It’s also an incentive for anyone else.

If I put the coin in and then leave the cart in the lot anyways, someone who wanders by is also incentivized to grab it and put it back, as they would get a free coin.

The system is actually somewhat elegant, if you return the cart you pay nothing and if you don’t you pay a small fine to whoever does.