Are you still talking about Streetwise in 1977 Traveller? Here is the key rules text:Why doesn't the player simply specify that the item they want is the dirt? If that's how their GM is running it.
Do you see what I mean? What heads that off? Why would they need to open the safe?
Streetwise expertise allows contact for the purposes of obtaining information, hiring persons, purchasing contraband or stolen goods, etc.
So what sort of contact does the player want their PC to make. With someone who knows where the dirt is? It's in a safe . . .. Or with someone who has the dirt? Those would be different difficulties, I think. (The latter being harder.)