Durwood, that the study's authors admit other factors may be at work is a hallmark of good science. They're forcing themselves to come up with other plausible explanations, then procedurally investigating them and concluding that they're less likely to explain the decrease in consumption than is the tax.
Which one(s) do you find unconvincing (it's possible to justify any explanation, no matter how farfetched, on the basis of imaginary "unknowns")? Do you have evidence of a motive for bias in the study, or is your accusation a product of the authors coming to a verdict which challenges your preconceptions?
The report directly addresses declining driving miles by performing a comparison with other provinces, which are likely to have a similar incidence of online shopping and sales of fuel-efficient cars. To successfully advance your argument, you'd have to show that B.C. has moved toward online sales or fuel-efficient cars at a disproportionate rate compared to other provinces (it's possible they have). Is that something you're prepared to do?
Finally, no one is making "a few bucks at the expense of the many" with a revenue-neutral tax. You may be surprised to learn that revenue-neutral taxation is being embraced by conservatives who accept the science on global warming, but resist the idea of expanding govenment to combat it. How to Tax Carbon, from The American Conservative:
Adopting a revenue-neutral carbon tax with regulatory preemption will do two very important things. The first is to provide a counter to liberal big-government policies that are already underway: conservatives currently are utterly absent from an important policy debate that will advance without their input. The second is to establish a tax code that is more pro-growth. Eliminating onerous EPA regulations and swapping out taxes on positive things like investment in favor of taxes on energy use would lighten the load placed on businesses and individuals by the federal government, giving the U.S. a larger and more vibrant economy to help absorb future climate impacts.
The good news is that this debate isn’t entirely theoretical. There are various forms of carbon taxes already in effect around the world. Perhaps the example most comparable to the policy described here is in the Canadian province of British Columbia. That province has had a tax on carbon emissions since 2007, a levy now set at 30 Canadian dollars per metric ton, with the revenue devoted to reducing other taxes.
Early returns on the policy are quite positive. A recent study found that the province’s gross domestic product growth has outpaced the rest of Canada, while its corporate income tax rate has been reduced to among the lowest anywhere in the G8 countries. Despite concerns that it might grow government, the tax has stayed revenue neutral and enjoys broad public support. Polling of business and community leaders by the Pembina Institute found 64 percent believe the tax has been a positive move.