Regarding the locksmith, I suspect he is already inquisitive, and quite likely to retail his info about our inquiries to Stavron if given the slightest opportunity, albeit while eliding details about just how much he told us about Stavron's business. On the other hand, if we involve him in the plot, he can sponge further money off of both sides (cash from us to bait the hook, and cash from Stavron as a finder's fee for putting him on to a potential investor in his gadgets). Not wanting to suggest to the greasy locksmith that we intend to kill S, we might even imply to the locksmith that the scheme is a means of recouping our supposed lost money via a scam, all of which he can later feign ignorance about if confronted by an angry S.
Is this scheme worth fleshing out further, or have a dud?