Step 1: Buy the seller (asymmetric knowledge went out the window with the internet. Everyone knows every car. You just have to find who "everyone" is. Put another way, ask yourself, "how did I get so lucky?")
Step 2: Get professional help (no, not mental. Find an Acura NSX-qualified tech to go over the car. It is a $200 insurance policy.)
Step 3: In addition to a PPI done in Step 2, I would insist on a recent alignment report coupled with knowledge that suspension can be further adjusted (i.e. with the car at current settings is there room for further adjustment or are you maxed out?)
Step 4: Get a Carfax. Who cares if it costs $40 bucks. You need to be able to trace the mileage. What? The odometer says 97K but the Carfax shows it titled with 129K last year? You can rattle the seller by asking for the receipt for the instrument cluster.
Step 5: Call every, EVERY dealer in a 100 mile radius. Give the shop the last 8 of the VIN and ask for details on work done. It works.
Step 6: There are several folks on this board that will be generous with their time. Find a way to give back to the forum (i.e. learn a ton and post, post, post)
So far, the above is what I have learned in the first year of ownership.
BTW, I passed on an 850 in mint shape to get my beater NSX. I passed because my BMW guru told me he would rather not work on the 12 cylinder motor. And, I got a screaming deal on what appeared to be a well-put together beater NSX. I skipped lessons 1-6 before I bought it. After I bought it, ego in hand, I had to start on step 6. And find another NSX - which I did.
Good luck!