My paraphrase: The answer is not easy. We give money to someone who does something that reduces emissions from what they otherwise would have been. For example, a hydro plant instead of a coal plant, or trees where there are none. But it’s hard to prove what would or wouldn’t have happened had you not paid. There are people who try to verify this but the proof problem remains. Also, there’s the permanence problem: will it endure (carbon emissions do endure)? I’m a skeptic but two offsets (expensive per tonne of carbon) are guaranteed: direct air capture of carbon and BECCS (grow plants, process them for fuel, and bury the emissions). Regarding policy options, I recommend not allowing offsets to be more than a small percentage.
