Gallup is more or less synonymous with careful polling. However, the final thing I'd add is that it wasn't just Gallup either. Russia claimed a total of 82.9% y

Gallup is more or less synonymous with careful polling. However, the final thing I'd add is that it wasn't just Gallup either. Russia claimed a total of 82.9% yes (if we assume 100% who did not vote would have voted no), Gallup found 82.8%, GFK (German polling firm) found 82%. The only 'outlier' (so much as 5% can be called an outlier) is Pew who found 88%. If any of these organizations' operations had been impeded in any way they would have made a big stink of it in their reporting. US and German organizations were not there to support Russia's claims, but to challenge them! But ultimately everybody's numbers ended up the same.