I'm looking at a couple of units. One had a bit over 200 hours and another has a bit over 100 hours. The 100 hour unit is being sold as 'new', the 200 hour unit is used, although they likely have very similar histories. I'm assuming that the 100 hours difference is fairly small, but I'm not sure. What do I need to look out for in a used unit? What constitutes low hours in a TC? What's the life expediency of a TC under normal utilization?