Weight and balance are the first things you can observe - just picking up a bass if it's heavy, it gets put back down immediately. Balance, same thing - I have no desire to ever own a neck diver again. Dead spots - bad ones, you can tell before you plug it in. If a bass passes those tests (few do)then I'll plug it in , tune it (dead spots can hide if the bass isn't in tune) and see how it reacts. Then, it's a matter if if I can get it to sound like the tone in my head, which rules out most of the basses that get that far. If you told me you'd buy me whatever I wanted (no budget limitations), and we headed into a GC, very good chance I'd still walk out with nothing. At Chicago Music Exchange, your wallet would be more likely to get dinged. still not 100 percent, though.
I have very particular tastes. I can build basses that I like, because I fully understand what I do and don't like, and I know how to tweak things so that I can iterate from the initial build to what I really want; anything off the rack at a music store has very little chance of being something I'd actually buy.
Short answer: I have a LOT of deal breakers.