Upgrade to Mavericks - Costs??

So back in March I tried to upgrade my MacBook Pro from Mountain Lion to Mavericks. Once it downloaded, I was unable to install Mavericks because it kept saying my Hard Drive disk is damaged. I got my macbook back to running mountain lion without any issues. A few weeks later, I ended up talking to an apple store employee about my issue with the upgrade. He said that when I was ready to try and upgrade again that I should bring in my macbook to the store and they will be able to do it there. I asked about the cosst to do it in-stores and the guy said there was no charge.

I'm sure that might vary store-to-store but can anybody help me? I just really want to know if I will get slapped a fee for the apple store people to do it for me..?