I´ve been living here for 8 years now, so I guess I know what I am talking about.
Usually Bolivians are very willing to help you BUT they are bound by silly laws and every fuel-station has a bunch of cameras, so they are (rightly so) afraid for their job. Yes they might lie about it, usually because the customers insists. To avoid a discussion he/she will simply say there is no fuel. (Which by the way can also be true as supply is random)

Gasoline is a major substance in the production of cocaine. In the governments fight against cocaine, this makes it a controled substance.
Very annoying, but that is simply the way it is.

Luckily you can buy gasoline just about anywhere. Just ask. Most small villages have a guy that sells it for 5 or 6 Bs.

Fuel-stations can often NOT sell fuel to a vehicle with a foreign license-plate simply because they do not have the permit to do so. They need a permit and special invoices (facturas).
Most systems are semi-automatic and need a license-plate, a ID-number and a name to get the pump going.
Here the only option is to bring a jerrycan and fill that.

At fuel-stations that do have those permits and invoices you pay about 9 Bs. (That is the official price for foreigners), so it is best (cheapest) to avoid those and find the guy who sells from the barrel. This is often cleaner as well.

When in doubt, simply ask. Yes there are ass-holes in Bolivia, but they are in every country. Don´t mistake ignorance, uneducated and scarred for their job for ass-holes. They are not. They are simply not as sophisticated as you because they only had 2 years of school.

I do motorcycle-tours in entire Bolivia (for years) and in my humble opinion people who have bad experiences only have themselves to blame. Change you attitude and your approach and wonders will happen. Even with police and fuel-stations.

I hope this helps you to understand this country a bit better.

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