It is difficult. I don't think I've been able to play a base that I've purchased in over 20 years. It's just the way it is for these more expensive basses that have very low distribution. And, even if you can try one, unless you buy that exact one, ordering one (even spec'd the same) can still result in quite a different instrument due to individual pieces of wood, etc., etc.
If you find that you are interested in a sort of '70's ash/maple single coil' type tone, then you can start perusing Talkbass for reviews and clips of Fender J's and, for example, Lakland Skylines or Sadowsky Metro's, etc., etc. and determine which of all these models speak to you (i.e., do you want a bass that sounds great passive, or will you always use a preamp, does 'single coil hum' bother you more than the postives of the single coil tone?, is the width of the string spacing at the nut important?, if you are going for a 5 string, is the bridge string spacing important? Are you sensitive to different scale lengths or weight).
Whew.... if you can try some different basses at Guitar Center that vary on these types of things, you can at least develop a template for what you like.
For example, at this point I only am interested in playing basses with 34" scale and single coil J pickups, with full spacing for 5 strings (19mm), and a 1 7/8"s nut width, a non compound relatively low radius board (or at least a gentle compound radius)... and the bass must have a relatively transparent preamp with a passive/active switch. So, that narrows things down quite a bit. That doesn't mean I'll dig every bass with that spec, but I'm pretty sure I will not dig any bass that is not of that spec.
This took about 20 years for me
