I think that what Vito meant was that they were not "murderers for hire". It was an insult to Vito that Bonasera (or anyone) could just stroll into his house,throw out a figure,and have someone killed. Bonasera asking "How much shall I pay you" added salt to the wounds by assuming that the Family was just a bunch of goons that would kill anyone if the price was right.
Vito even wondered what he had done to be treated so disrespectfully. Bonasera was just an out of touch immigrant who figured that one gangster was the same as the next,and that they would do anything for money.
He didn't catch on to the fact that if He had treated Vito as a friend from the get-go,and his daughter had actually been killed,that Vito would have ordered the murders of the two guys responsible as an act of friendship,and would have been insulted by any offer of money.
Excellent point. Yes, no doubt that Bonasera had insulted the Don greatly by essentially treating him and the family as if they were just common street thugs. Under the circumstances, I think Bonasera was fortunate that Vito was not the vindictive type, prone to holding petty grudges - or at least that he was in a good mood on his daughter's wedding day - else the undertaker might just have unwittingly made a powerful new enemy for himself that day. Not a good place to be at all.
