TRUSS ROD!!!

If it's just the 6th fret that's buzzing, then the problem is not relief. If it's also buzzing at 4 and 5 then loosen the truss rod a smidgen.

 

You may or may not need a truss rod asjustment. With a straightedge and feeler gauges, you can sort that out quickly. Without the right tools, it’s more of a crapshoot.

 

A high or low fret, most likely.

 

A high fret, low fret, a fretboard hump, a kink in the string - there are a few possibilities. Start by looking for fret un-eveness.

 

3 alternatives:
1. remove frets, make fingerboard flat again, install new frets.
2. replace 6-th fret with taller one and level the frets.
3. rise the fret by partially removing and hard glue it so it doesn't go back into a slot.

 

It sounds to me like it needs a routine fret leveling job, which may include tweaking the truss rod. I guess the guy at Sam Ash doesn't do that work. It's not likely that the 6th fret alone is low enough to require re-surfacing the whole fingerboard. Possible, I guess, but not likely. A fret that's 0.002" high or low can cause a nasty buzz. That's easily corrected by a routine fret leveling job. You need to find a Tech/Luthier who does fret leveling.

 

Is the bass new? Where did you buy it? Is it under warranty?