Every once in awhile we will receive a hard drive that has been opened by someone.
If this someone was a reputable data recovery company then there is no issue with this. If however this person was a friend, or at another company that wanted to have a look at what was going on inside the drive, this is an issue.
There should be no reason for anyone to open up a hard drive in a non-clean room environment. A hard drive read/write head is 7 nm above the platter when spinning. Smoke particles can sometimes be up to 10 nm in size. Any contamination within a hard drive will cause the heads and their contaminant to scrape against the platters thus scratching off all of the magnetic substrate that holds your data.
Opening up a hard drive just to see what is going on will damage your data. More often than not we will need to get a hard drive into clean room and clean it Before spending it up, which adds extra expense to your recovery.
In short, do not open up your hard drive chamber.