It has become more common for dealers to charge for fault detection, to avoid time spent being unable to reproduce customer's problems - some people complain about bizarre things.
If you have a problem, the key is to be able to demonstrate it to them - eg show them in the car, take them for a drive if needed so they can clearly understand it.
With bluetooth problems, that might be hard to reproduce, but fixed through a software update, I'd ask: is there some other problem which is easy to reproduce that would also be fixed by an update that you could approach them about instead?
However, if the first thing they are saying to you is how much an investigation will cost, that's not a good sign.