I've ordered from buy.com precisely two times. The first time was me ordering a retail box HDD kit (I forget why, but I did have my reasons; it may have come with some free AV software at the time.) Instead, they sent me an OEM drive.
Fast forward to last year, I ordered a copy of PDO, and the damned game couldn't have been more obviously resealed, and the DVD-security-no-one-jerked-off-on-this-disc seal was also missing.
I'd stay clear of buy.com. Something just ain't kosher with that outfit. Also, I've never heard of sparco.com, check their Bizrate.com and/or BBB rating if you're unsure.