I've never purchased anything through their eBay store, but I've purchased LOTS of equipment through DFS in the past. I'd recommend them.
I have had a few issues, whether it be a failed HDD on a laptop, a non-functional keyboard, etc. but Dell always addressed it immediately and there has never been any additional expense. A couple of times they sent me the wrong laptop, but they take care of it quickly and it doesn't cost me anything to exchange, and one time they sent a replacement that was better than what I ordered.
They now have "tiers" of quality of their refurbished stuff. I'd recommend buying from the top tier. Most of the stuff looks/feels brand new. One time I unknowingly purchased from their lower tier and they sent me a laptop that was nasty dirty, but they addressed it quickly.
I'd imagine going through their eBay store you get the same service, but you might also try to go directly through their website. There are often 25-30% off coupons (sometimes on their home page or Twitter feed, email list, but most of the time on deal sites), so you can really find some good deals.