After going back and reading the "other side", so to speak, in depth, I realized that the argument doesn't sound as strong as I initially thought it was. Searching about the issue on Naver gives you back about ~10 topics calling out SISTAR and exactly three posts defending them, one of which is just an opinionated speel so I'll be not including.
Skip the first part if you're already familiar with the issue.
I'm sure you can google the topic to find translations, but the gist of it basically is that SBS's 'One Night in TV Entertainment' ran a report about companies buying out 'brokers' mostly running their server from China to manipulate digital music charts.
For $100,000 USD at minimum, these brokers will use hundreds of thousands of IDs they've registered on these music websites and download the songs of the artists they're working for. In order to not make it suspicious, they'll go slowly and work with a group's debut. For example, they'll launch the group's debut album into the top 20, their next mini-album into the top 10, and finally their next comeback with a chart ranking win.
The anonymous broker interviewed on the show mentioned that he recently worked with a rookie girl group to manipulate the charts for them, which eventually earned them a win on 'Inkigayo'.
The conditions he named basically were:
1. Female artist that won #1 on Inkigayo this year
2. They've been involved in this manipulation since debut
3. Most of their digital downloads were from thousands of people in the early morning
4. The dominant age group was those in their 40s~50s
Netizens narrowed it down to the Wonder Girls, miss A, T-ara, SISTAR, and f(x) as the girl groups who recently won a trophy on a music program. Wonder Girls was dropped since they haven't been promoting, miss A was dropped because they won a trophy immediately with their debut, T-ara was dropped because they've already won several trophies, and f(x) was dropped because they won a trophy last year.
That left SISTAR. Their numbers showed that there were an overly large amount of search requests around the time they won, which all dropped a few weeks after they won. Most of their searches came from males in their 40s and 50s. In comparison, other girl groups showed steady search graphs with most of their searches coming from women in their teens and 20s.
Hello Venus shows a similar graph style to SISTAR but they never won anything so they were dropped as well.
Now what the other side is arguing is basically that these charts are unreliable and there is a chance for technical error.
Yeah, compared to those popular artists, SISTAR's graph definitely looks off and suspicious, but this side argues that there are just as many other artists (all of whom ranked high on digital charts) that don't have the company/money/power to hire these broker services that have graphs looking just as messed up as SISTAR's.
[Lee Ha Yi]
[Run to You]
[Park Ji Min]
How would the "Run to You" graph be explained as well? The song was released in the year 2000 so why would there be a sudden jump in searches on July 24th? You can't say that LEDApple, who has a Swing version under the same title, bought a broker service for it because LEDApple walked away with miserable results on the charts, and it wouldn't make sense for DJ DOC either since they haven't promoted in years.
Another point is that these graphs only show search trends. Just because someone searched their names on the music sites does not mean they bought their music, and just because someone bought their music does not mean they searched their names to find it, which leaves a lot of room for technical errors on these graphs.
The final argument is that SISTAR's achievements were consistent across the board on not only Melon, but other popular digital charts as well for a very long period of time. Netizens are arguing that Starship Entertainment couldn't have possibly afforded the broker service for each of these charts at the length of time in which they were ranked considering the costs.
Source: (1) (2) (3)
Again, there is no clear answer. The overwhelming majority believe that SISTAR did indeed manipulate the charts through these broker services, while the minority argue the points listed above.