Northern California - I think our LBS screwed up. What should I do?

My husband and I bought two 10-speed carbon fiber bikes from our LBS. He elected to go with a smaller cassette (i.e. the biggest cog is smaller than stock) at the time. But later, he regretted it because he was not as strong as he used to be or would like to be and all our riding involved hills. So, to give him a surprise (before last Christmas), I took his bike in to the same LBS, and asked them to switch his cassette to the standard size and went for an upgrade (to Ultegra). I paid for the new cassette and they did the switch. On our next ride, my husband was happy to find that riding uphill suddenly seemed easy on his knees before I revealed the truth.

Fast forward... We didn't ride a whole lot, but when we rode, he always seemed to have shifting problem. We took the bike in (the same LBS) for tune-ups a couple of times, but the problem never went away. Finally, he took it to another shop, further away but highly recommended. Yesterday, we got a message saying his bike got a 9-speed cassette with a 10-speed shifter. We had never suspected it! Who would have thought our LBS put a 9-sp cassette on a 10-sp bike?! I don't know that much about bikes, and that's why I trusted them.

Anyway, I'm going back to the shop today. My question for you guys is, what is a reasonable expectation? Am I supposed to buy a new 10-speed cassette or do you think they should replace it for free? There might be other ways to get this issue fixed (e.g. changing the shifter), but I'd like to keep it a 10-speed bike. Thank you.

I think if you bring it in again the LBS will fall all overthemselves apologizing for such a stupid mistake. If it were my store I'd replace the cassette for free (maybe charging the incremental cost between 9v and 10v that you would have paid for the correct one in the first place).

edit: I don't actually have a store, just making a point.

Did they give you back the original 10-speed cassette? Or you just pay for the difference in price for the upgraded Ultegra cassette? I would ask them why they put a 9-speed cassette when they know they took out a 10-speed cassette...and then ask them to put on the right cassette. Could be just one of those stupid mistakes, so I would ask first...and then demand if they try to blow you off.

If you have the original receipt with the new cassette part number on it, it would help you make your case immensely.

Thanks for the input guys. I guess I should have counted the cogs after that switch, so I wasn't sure what to expect from the bike shop. It turned out when I went in today that the manager was surprised that such a mistake was made and was willing to switch it to a 10-sp cassette of the same size. I don't have the receipt, so have no idea what I paid almost a year ago. I guess it's in their system and we can work it out. So, it's cool in the end.

Glad it had a happy ending. That's exactly what they should have done.