is it easier for companies to hide sajaegi today?

No it's much harder, because the charting services are very detailed and mostly transparent. Plus fans being ridiculously obsessed with charts make them pay attention to and overanalyze things, they'd be the first to call out a change in charts even if it was a legitimate change

You just engage one of the professional companies that offer it as a service.

K-pop in the YouTube era: 'Sajaegi' - The Korea Times

No there are just more routes to payola than a song suddenly turning up in the top 10 on the real-time chart

If you think about it they weren’t very tactful back in the day

Not really. We don't see more nugu soloists reaching one million ULs out of thin air like they used to