Sorry to hear you are having problems. At 800 miles, a Viper should be like new unless the prior owners didn't store the sled properly. I bought an 2002 Viper w/642 miles on it that sat three years in a covered trailer after the 62 year-old owner died of a heart attack. Son gave up the sport and I bought the 2002 Viper and an 2001 SXR 700 as a package.
SXR had 2900 miles, and was beat. The Viper showed no wear, but much of the aluminimum was covered with stained w/corrosion. It took some work but I got her up to snuff. Hopefully the 800 miles on your sled is accurate. Look for wear on the track, skis, grips and running boards. Seen lots of "low mileage" sleds that showed significant wear in these areas, and my thought is that they either disconnected the speedo (not likely on Vipers, thought they could have changed the instrument pod)
What kind of issues are you having? Post about your problems and maybe the forum can help. Incredible amount of knowledge and experience here....