I once brought in my amp to check out a bass. Since then I've decided to save on the back ache.

The last time I bought an instrument (Friday as it were), I knew exactly what I wanted to look for. I had just got the new Musician's Friend cataloge in the mail a couple of weeks ago, and saw a bass that looked interesting. So I went on down to my local Dean dealer, found the bass I saw int he catalog, played it and walked out hte door with it... (I payed for it of course).
Sometimes you just get a feeling about an instrument. I try to go with it if I have the money.