I had a nightmare used speaker experience with a Thiel CS3.7. It turned out to be fun in the end because I made the speaker perfect, but it took 2 months to fix it all.
1) Find out if the drivers were ever replaced. If so, by whom.
2) Are replacement drivers available to buy?
3) What amp was used to drive the speakers?
4) Is the warranty transferable?
5) Can the speakers be serviced at home or does it need to be shipped back. For, example my old Revel Salon 1 needed to be shipped back to Northridge, CA for a simple driver replacement. They said they need to re-measure the speaker after the new driver. That was done 2 times, and I will never buy a Revel again. My Thiel was messed up by the seller with a bad repair. However, there is 1 guy left providing drivers and advice on Thiel speaker repair, so I was able to do a home repair to make it perfect.
BTW - I could hear 1 issue with the speakers when I got it home. When I measured the speakers with REW software a whole can of worms opened up. The guy at this place helped me measure and pinpoint exactly the spots that had issue, phase, crossover, driver. It was a mess.
Digital Room Calibration Services, Convolvers, Headphone Filtersets (accuratesound.ca)