The number one in a business relationship is to be clear about money issues. Friendship may come in addition. A lot of people think that asking for money will hurt the relationship but the opposite is true.
Yes I think this answers my question quite distinctly, asking for the agreed amount should not have resulted on what happened. Even if there is a misunderstanding on any side, it should have resulted in negotiations, not an immediate accusation and denial of work done.
It's all in all pretty disappointing.