FWIW - I did a lemonade stand as a kid and charged $.05 per glass. We (brothers/friends) would keep a jar with about $.75 in change on top of the table.

Everyone felt bad for us and tipped us $.25-5 per glass - avg tip was $1. We could not have charged $1 - we tested the price elasticity of demand. But, they felt terrible we never had any money in our jar.

Just saying tips make a difference.