That is up to you. I have dealt with used tanks before and they have worked well for me. But I did go with a new one this last time around. It was my 4th tank and I had been in the hobby for 6 years and knew that I would be in it for a long time. I have had seals that hold well even though they are deteriorated and peeling along the edges. It is understandable that you are concerned about a leak in the tank but it is a risk that every fish keeper has to deal with regardless of the age of the tank. When you put any tank in your house you risk it leaking or spilling water. Even tanks that are new could leak. There are some ways to mitigate your risk.
1) you need a stand that supports your tank perfectly, no exceptions (This in my opinion is the cause of most tank failures)
2) treat the silicone nice. Even a new tank can be ruined it you scrape the seals every time you clean the algae of the tank.
3) If you are still concerned, be proactive and get some form of leak detection sensor.
4) if you have a choice in the flooring (remodeling or new I would not remodel just to place a tank) choose a tile or vinyl that can stand up to some water. This is a good choice regardless of if you have a failure because you will get water on the floor.