Thanks for all the replies.
So interesting comments and also a complete mixed bag.
I agree that most store basses won't be set up to test properly anyway (they look like they haven't seen a screwdriver or allen key since being taken out of the box) and the thought of trying some show off slap or fancy jazz is a big no, so yes, taking plugin miniamp and headphones is a good idea. And a strap. PMT in Bristol used to have a small room you could have a tryout in (tbh they should stick the guitar buyers in there too, save us the suffering!)
I can see that if you prefer say, a jazz, that buying blind would be fine as you know what you should get. But how do you know you like a jazz without trying a jazz first? Or a Stingray, or an Ibanez.
So I bought a Squier jazz to see and now I know, but it was a gamble. I've also an SR which I bought because I love the look and thankfully love playing. So thats 2 for 2.
I should have gone to the SW bass bash!