If I may respectfully correct you here.
Actually, sandbagging is specifically not allowed.
Sandbagging means “actively manipulating your rank to deliberately misrepresent your skill”.
It is not always easy to prove (or even decide) if someone is doing this. If a person sets out to have a lower rank than their skill with determination, they can probably achieve it in a way that we can’t police.
However, we do attempt to prevent it where we can.
There is a conundrum about this that relates to unranked games. Unranked games are allowed.
Playing unranked is not manipulating your rank. It is simply playing go without affecting your rank.
It was agreed in another thread that Dwyrin is welcome to play unranked at OGS. However, he is not allowed to play at a skill level below his actual skill in ranked games (IE he can’t do “Basic Series” vidoes in ranked games).
When Dwyrin plays unranked here, his rank will not change. This means that it will not reflect his skill. Is that sandbagging? Conceptually possibly it is, but practically speaking, there is nothing we can do about that. Either you are allowed to play unranked, or you are not. If you are allowed to play unranked, then people can have accounts that do play unranked that will not reflect their skill.
If you want to play with people who’s rank reflects their skill, don’t play unranked games.
If you play unranked games, you can expect that the other person’s rank is not reflecting their skill. It seems obvious: they (like you) play unranked, so how could their rank reflect their skill?
If you suspect that someone is manipulating their rank deliberately, please report it.
If you simply feel that someone’s skill is not reflected by their rank, but have no evidence that they are manipulating their rank, please at least do a little homework before reporting them as a sandbagger.
There are legitimate reasons why someone of lower rank than you beat you, it doesn’t automatically mean they are sandbagging. A person who is on an improving trend is one such case: their rank will lag their skill.