Just bought a used 2004 Accord and had the check engine light pop on on the way home. Errors came up as engine misfires. Dealership said it was most likely water as they had just hosed down the engine before we bought it. They reset the error, we drove home and it popped on again. Took it back and now they're telling me it was because the ECM needed to be updated. Am I getting shafted? Any suggestions?

Edited to add: It's a V6 sedan.