The quality of materials. The ply is super resonant and light weight. The craftsmanship is pretty impeccable and they just out-play their cost/value (tone + volume = $$$) ... In terms of the Clevelands, specificially, they're arguably superior to the coveted American Standard basses because of the more comfortable 42" scale length. (not to mention, my AmStd is heavy AF). Quality control is on point (no reports of a bad NS bass), and resale values stay high. Win/win/win.
Theses are fantastic basses (I owned one) and this is a below-market price. Repaired by the highly esteemed original builder. A great acquisition for the lucky new owner. Go get 'em, tiger!