I would highly recommend looking at refurbished they are as new in almost all cases and usually any bugs or recalls have been sorted out and you can save money in the process.I had three refurb Nikons D3300 D90 and D7000 all functioned and looked brand new.The only thing different was an ugly white box marked Refurbished instead of the pretty gold box.
You don't think it would be worth spending extra few hundred on the D810? I've been doing lots of research comparing the two and I'm still not sure!No worries at all. One of the best cameras on the market, 3+ years and counting. Even if you have a problem with a used copy, Nikon will fix it. But buy wisely, with confidence.