[quote name='EssentialTension' timestamp='1329655255' post='1545338']
There's lots of good advice here but it is quite simple really - you are testing the bass out, not the shop testing out your bassist skills.
Playing songs/tunes is the very last thing I'd do. Inspect the bass: finish, fretwork, tuners, etc. does it tune ok? Play every note on every string and listen to it acoustically, are there any dead spots? Does it intonate satisfactorily? If the bass passes so far then plug it in, an amp of your choice, with controls flat. Repeat the every note, every string trick. If you're still happy maybe play some tunes, in different styles, maybe adjusting the tone. Play with right hand near bridge, over pickup, near fretboard. Are you going to need different strings? That needs to be factored into the cost. Etc., etc.
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Exactly this. You're not there to impress the saleman. But even if you were, if he knows his job, this is likely to impress him more than playing a load of technical flash stuff without actually checking out the basics.