I've bought from DiveTheAbyss 4 or 5 separate times over the years, never had a problem. Everything was brand new in the original package. I'd happily buy from him again, but I now have LDSes that carry or can get the older Apeks regs, so I don't need to buy mail-order or eBay.I've seen this stuff before. Got spooked because there was a horror story online of someone who had a problm, went the registered adress and there was nothing. Made me more than nervous. The DS4 was my top choice for first stages.
Don't forget, there's always 2 sides to a disagreement. Example: one of the guys I worked with bid on something on eBay, then was upset that the seller wouldn't send him the item to preview BEFORE he paid for it, and AFTER he'd won the bid.
Also, (due to the nature of the Internet) if his IP address changes, it could take up to 4 days for it to ripple through, and his site would be dead as far as you could tell. Anytime you hit a totally dead site, check back a week later. Further, if a site appears to have been taken over by DomainPark or one of the other domain sellers, it could be due to an address change that hasn't finished rippling down. Again, check back a week later before you write 'em off.
My 2psi worth, your SAC rate may vary.