I will not dive with a bottle that I have not analyzed personally, or witnessed being analyzed. You will be instructed to do just this in your course, and should not deviate from the practice. It takes less than a minute and is essential to your well being.
Every shop that I frequent to have my cylinders filled has an analyzer on site, and I’m happy to use it. I’ve got a rather hefty trimix analyzer at home that I will travel with as the situation warrants, and always travel with a small O2 analyzer.
I bring my O2 analyzer on my long distance travels. If I’m on a live-aboard, for the first fill I’ll use the boat’s analyzer and then confirm the reading with my own. If they are in agreement, then I’ll continue to use the boat’s unless there’s a rush on the unit. In that case I’ll just use my own, and have a similar approach at land based operations.
I did not cast a vote in your poll, because the wording in imprecise.
I could not answer “ALWAYS” because I do not always bring my own to local shops.*
I NEVER trust what I’m given without positive verification.
I do not patronize SKETCHY local operations. While traveling and using an unknown operation, I’ll have my own analyzer for O2, (or trimix should the need arise), but if a place seems “sketchy” to me, I’d most likely be concerned with the possibility of other contaminants.
* I own a lot of tanks. Sometimes the mix label will fall off of one or more of them. I don’t simply pick a label off of the floor and assume that it came from the tank in question. I’ll take a minute and analyze the cylinder, then relabel it.