Venting refrigerant is illegal in most of the world but it's almost impossible to enforce and compliance is typically quite low (good data is, as you can imagine, difficult to find). CARB in California now requires owners of large refrigeration systems (>250 lb of charge IIRC) to report all refrigerant recharge to the state so at least there's some efforts underway.
Note that the vacuum pump is often a free rental from the auto parts store, I don't know why they can't/don't rent the recovery equipment.
When you put it back together you can pull a vacuum on it, close it off and make sure it stays that way overnight. But you may still want to have a professional shop test with higher precision than whatever gauges you use.
1. Methane is 1900 ppb in the atmosphere[1], refrigerants overall are ~12.5 ppb -- so a lot less out there to detect. 2. I think methane leaks tend to be from single, continuing, large point sources -- coal mines, oil wells -- whereas refrigerants are usually from these distributed small point sources which happen once. So by the time you detect it it's too late to intervene.
[1] https://www.noaa.gov/news-release/increase-in-atmospheric-me...
So what if they are picking too-low-hanging fruit initially? As long as their process can in principle scale to a point where genuine reductions are possible. And they do actually enter a legitimate certification process fairly soon. The certification authority will then become responsible for proper accounting.
In the mean time, they are asking for investors' trust without verification. Not ideal, but not unreasonable for a PoC / MVP.
A lot of the newer refrigerants are much safer for the environment, but you are still allowed to recharge and buy older refrigerants. Only the manufacture of new refrigerants is prohibited.