The more I read this the less I think it's about chainsaws. Both of these women seem poorly trained in male etiquette, and the boyfriend, even if he is a 300lb brawling concrete worker, is a schemer. There were two passes where this deal should have been cut off.
First, boyfriend asks SIL: "Would you ask your sister if I can borrow one of Outdoor's saws?"
SIL: "Why, scared to talk to him? I know better than to get involved in a tool deal, here's his number. Besides, maybe if you'd stay out of the topless bars for a week you could buy a saw."
Or, SIL plays the dupe, but your wife says: "I'm sorry, Sis, I don't think that's a good idea. Outdoor is pretty particular about his saws, and if Nick messed it up I wouldn't want to be involved. Besides, didn't he just turn down a great deal on a saw? It's too bad Nick can't afford his own tools, but I think he should handle his own business and not make it our problem."
Too bad, a missed opportunity for both of them to have your back.
Jack