If you are going to the store with the intent to purchase, then you should take a few tools. I have a small kit I carry with me that has the following:
1. Cardinal HSDC-20 digital hanging scale - Let's face it, weight is going to be a comfort factor with any instrument you buy. The GC guys are known to lie about the weight question and you may not have the accurate "calibrated arm" that you think. Take the guesswork out of it with this.
2. Mitutoyo micrometer model 122-126 (or equivalent). Sure, the spec sheet says that nut width is 1.75 inches, but are you willing to take that as gospel? This guy will help you establish the truth.
3. Mabis Signature Electronic Stethoscope - Do you really know where those dead spots, defects, and other tonal pockets are located in that prospective new bass? You simply can not afford to guess. This will allow you to get an accurate map of the tone woods with your ears.
4. Lisle 52500 Mechanics stethoscope - While the standard electronic stethoscope is great for getting the overall picture of what is going on with the body woods, inspecting the neck and fingerboard requires a more precise inspection tool. Before making that purchase decision, know exactly where the dead spots are located.
5. Lisle 68100 Feeler Gauge Set - How well is it put together? A few quick checks on the assembly points with this and you will get a good picture as to the craftsmanship of the instrument.
6. Fluke Ti-10 Infrared imaging camera - If you are buying an active bass, you are concerned with making sure that the electronics are "top-notch". Cold solder joints, substandard electronic components, and faulty assembly can mean problems down the road. By looking at an IR image of the preamp while it is in action, you will be able to pinpoint any areas of the circuit where abnormal operating temperatures may indicate problems that will cause excess battery drain.
7. Fluke 117 Digital Multimeter - Passive electronic components in the preamp need to be checked to ensure that they are within specified tolerance. Any substantial deviation and the preamp may not perform within design limits, often with an impact on your tone. This will allow you to carefully test each component and to take voltage/current readings while the preamp is in operation, ensuring that it is performing as designed. Also, this is useful for routine continuity checks on passive instruments.
8. Kassoy L-820 Jewelers' Loupe - The finish may look fine to the naked eye, but small defects that may eventually become checks and visible surface flaws can only be identified with a more discriminating look. The loupe will allow you to find these with ease.
Each of these tools will allow you to make a detailed examination of the instrument under consideration. Make sure that you take the time to use them thoroughly.
OTOH, I heard from an owner of his brand that Roger actually uses these tools on every bass that comes out of his shop, so if you are buying one of those, you may be able to skip all this.