[baddox]

Not only can people change metadata, there's also a good possibility that a scene group and an innocent home user would make separate rips of a CD that would be bit for bit identical. There are checksum databases online that enthusiast rippers can use to verify that a ripped CD is identical to the results other rippers have achieved (i.e. no errors occurred in the ripping process).

There is a whole technical community dedicated to getting quality CD rips. As an example to how serious people are about this, one technique is to disable or circumvent the optical drive's buffer and make multiple read requests to each area of the disc to help ensure that the correct data was pulled in.

http://www.accuraterip.com/

http://www.digital-inn.de/forum14/