I buy refurbished stuff all the time and have never had any problems. They carry full manufacturer's warranty and have gone through quality control twice.
It's a good deal, but the player isn't all that great. It has good deinterlacing - thanks to the Faroujda chip - but the picture is very soft and the build quality is poor.
I would say you'll be hard pressed to find a better player for $99. While the 910 has it's issues it is far better than any player you could find for $99 or less anywhere else. I say go for it, you have 30 days return from ecost and 90 days warranty from Denon. I would take a Denon refurb over the other extremely cheap stuff you would find for under $100 out there.
I picked up a 910 refurbed from Ecost, I like it so far. Haven't had it glitch yet. I don't have an HDTV, so to me the picture looks very sharp on my WEGA.
I beleive it was the 900 that had the soft picture and flicker issues and the 910 addressed these problems quite well. You will see 910's pop up on ecost from time to time, usually around $130 making it them a very good deal. I still think the 900 would be a better player than most other $99 players out there even with the soft picture. The 910 however is a noticable improvement and offers even more bang for the buck when they are available for $130.