If you were unsatisfied with the bass that arrived you'd be within your rights to back out, I'd think.
I think that is true only if there is something wrong with the bass. For example, if I represent that a bass is in a certain condition, and you receive it and it is not in the condition described, you would be within your rights to back out.
If the bass is as described and you just don't like it, that's another story. For example, let's say I trade you my jazz bass. You've never played a jazz bass and you find out when you receive it that you don't like jazz-width necks. Should you be able to back out of that deal? I don't think so.