Thanks for your comment.
As you say, lab experiments inevitably have their limitations. I don’t think that makes them unreal (in the sense that their results are invalid or worthless).
Field experiments also have their limitations, and I think that well designed lab experiments can and do provide insights.
There have been many experiments on voluntary donations (and indeed other pro-social behaviours, like littering), some with a camera, some with ‘eye’ imagery, but they tend not to replicate very well.
I suspect the best we can do is not to take any single finding as the new gospel, but treat it as a piece of evidence, that adds to our body of understanding.