Honestly, recent price change really has hurt fairly "new" pre-owned sales. Many options and all after market stuff (e.g., wraps on this car) are worthless on resale. I can order a S75 exactly how I want it for 78,800. Counting 1000 referral and 7500 tax, that's basically 70k. I would only pay low 60's for a pre-owned S75. 60-65k is the fair price for these cars, assuming people actually like this particular car, and you better sell sooner than later. When M3 75 comes out, is much cheaper with more range and the same or even better tech, you are going to get major ding again.
Honestly on something this new, try to get a trade-in appraisal, might be as good or better than what people are offering. In that case, makes the sale so much easier.