Is it customary for auto dealer repair garages to charge for parts before installation?

My check engine light came on my 2002 Honda Civic (100,500 miles). The dealership repair garage charged me $50 to diagnose the problem (get the engine code). Come to find out, it was something about a leak in the charcoal canister in the emission line. Then they said because my car was so old, they couldn't get the exact part I needed because they're not made any more, but they could install a "kit" which cost $90. It was kind of like a work-around "kit" so they could byp the canister. They didn't have one in stock, but would order it if I paid for it beforehand. Then I'd only have to pay the $130 for labor to install. However, they couldn't even guarantee that this would fix the problem. I have to have this fixed or my car won't p inspection and only a Honda dealer can do it. I wanted to know if that is a reasonable price to pay for a diagnostic test? It is the usual practice to charge a customer for parts even before they are installed? Should I be wary because they are so unsure about the repair? Any other advice?