I've actually purchased over 500 ebooks (yes, I know I'm a glutton
) and have not had any errors with the ebooks I've purchased (other than typical typos that you can find in any paperbook) other than the issue with Overdrive. Even the ebooks that I've preordered have been available on the day indicated. I have to agree with a previous poster that things seemed to have gone downhill since the Overdrive debacle. I would even take it one step further and say that they had already started to slide when FW bought ereader and started pushing their proprietary format.
As for customer service, I've sent in questions on two separate occasions. Each time it took several days for them to respond. That's probably the poorest response I've ever received from an online vendor and I do a lot of shopping online.