Drive it. Take it slowly to 70 MPH or so. If it wobbles on the way, back off, you spotted it, walk away and fine another one. If not, it doesn't have it.
If you buy new, you know it's solid. Personally, I'd get a Rubicon, it comes with stuff that would cost you many thousands to add. The locking hubs are around $1200 per axle, and it comes with the heavier Dana 44 axles. Trail rated, take it out and have fun.
A much older model is another story, if you want to build one, or even buy it built. The old ones don't get cheaper than around $6k stock, or $10k lifted, unless you run them in to the ground.