First, really appreciate your time and the opinion.
B is not A's subcontractor. He is his friend for years then in 2009 helped A for some office duties. I'm not sure if there was a contract between. But it does not sound like.
Theoretically if I had not paid or paid insufficient should not be A's excuse of not paying B. Am I right legally?
I want to help if it's going to hurt me. Also it's like I take the B side if I show the record. A to me now more like a流氓+無賴. Do anything against him may bring some bad result. Also I'm not sure where the proof B is taking to? It could be a record against me also if goes to elsewhere. Of course if so B won't get money.
For all the thoughts above made me hesitant…