Why did Sonny trust Carlo enough to introduce him to the family and then sour on him?

From what I remember from the Novel, Carlo is in some kind of trouble with the police when he comes across Sonny, who uses his connections to give him some kind of sanctuary, and eventually absolution. It's quite ambiguous what Carlo has done...

At this point there are no hostilities towards him, so no reason not to invite him to a party: he's not a Cop, he's come to them for help... The Cosa Nostra appropriate social meetings in order to conduct business without suspicion, that's their basic MO with this type of thing, so it's not just a party for Carlo, it's an introduction.

Vito immediately takes a disliking to him, but not enough to do anything drastic; he just suspects he's not what he seems. Sicilian tradition however, of which Vito is Orthodox, forbids the interference of a father in a relationship bonded and destined for marriage.

It's not necessarily explored in the film, but Carlo is secretly only married to Connie to gain entry to the Corleone family; and, further to this, uses his position of patriarchy over Connie as leverage against the Corleones.

He subtly blackmails them throughout that if he doesn't get his way, he will use violence against Connie; this is why Sonny, and everyone else, comes to loathe him.

I may be wrong but I read somewhere (God help me because I can't remember where I read this) that the reason Vito didn't want Carlo included in the family business was because Carlo wasn't Sicilian...that he was from another town in Italy and somehow didn't approve of the marriage. As punishment to Connie, Vito didn't interfere whenever Carlo would beat up his daughter making a statement that he never liked the idea of his daughter marrying him. If that is the case, why would Sonny introduce Carlo to his sister if Vito wasn't too happy with the relationship.