If he was a mnaufacturer then he would more likely be asking you if you were interested in 5,000pcs...
Generally, unless you can burn several hundred DVDs in a month, you do not have the need to buy directly from the manufacturer.
On the note of the overprinted discs, I recently picked up a mixed spindle of 100 CD-Rs, made by both CMC and Ritek. The discs were all overprints, and I got a REALLY good deal on it! I took it home expecting lower quality then average (and I didn't know there was CMC in the spindle when I bought it!). I was surprised to find however that all the discs, even the CMC discs are performing VERY well so far! Not that I want to give the wrong impression about CMC, they are still unreliable... but it appears that the overprinting process doesn't reduce the quality of the media, at least in an overly noticable way. I still won't be using these discs for ANYTHING remotely important, but they make nice cheap one shot "throw away" CD-Rs, which is what I bought them for anyways!
So long story short: Overprinted discs are not neccissarily bad, but burn with caution!