source? why would anyone care about source?
Only perhaps if I'm too lazy to care about it, I'll just be like "yeah, it seems like he knows what he's talking about, but I don't, so that doesn't mean much".
Definitely the structure of the argument.
More than anything, though, the motivation behind the argument. If the motivation is invalid to begin with, then the argument can be good and I still won't give it too much credit.