This is not sandbagging. The players know what they're getting and the rating system does too.

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Occupy Babel!

That wasn't my impression. I felt that the self ranking worked pretty well. I for example report in with one or two stones below my KGS rank.
The only significant ranking problem I saw on my last tournament was a player who played his last game of go several years back in China, and people didn't know how to convert that to an EGF rank.
But I'd say the problem here is that the math behind the EGF ranking system sucks. IMO if I report a new rank when at a tournament that shouldn't reset my EGF rank, but my results from playing stronger players should improve me quickly without hurting them too much. I'd love to see EGF use WHR instead of ELO. ELO just doesn't work on sparse data sets.

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Sanity is for the weak.

I agree with you that generally the self ranking generally works pretty well. What I meant was that overranking occurs much more frequently than underranking/sandbagging. I checked the EGF stats of my opponents who have been playing regularly on tournaments for several years or who have played several times in the last months, and from a total of 33 players 27 were ranked fine, five were overranked, and only one was underranked (i.e. self-ranking and rank from rating differ by at least two ranks/200 pts), and this one was previously overranked, so it might just have been a correction that the EGF system doesn't approve of.

I also agree with you that the EGF rating/ranking system kind of sucks (I just remember the Dutch report that Herman Hiddema has mentioned), but at least for regular players it gives a quite good approximation of playing strength.

Since I mainly play on KGS, and have recently started playing on IGS and Tygem as well, I was somwhat at a loss as to what rank I should be, as some of the rank information on http://senseis.xmp.net/?RankWorldwideComparison is pretty vague. Well, for Tygem, definitely. I started at a rank that I thought was somewhat below my actual level, because I wanted to experience the difference in strength/ranks for the different servers. After an initial period of 'sandbagging', the situation is normalizing. I guess it's what Kirby described as earning your rank. Playing against players which are weaker than you is not all that fun, because they usually can't assess the game situation very accurately, and play on long after the point of no return. I spent most of those games as a 'sandbagger' wishing my opponent would just resign and be done with it. It wasn't fun at all. I guess the most fun games are playing someone slightly stronger than yourself. Concerning the psychology of sandbagging, I think Tchan stated some excellent reasons as to why one might sandbag.

I'm a beginner who has played after the point of no return and I think it's natural (I'm not implying that you don't). Maybe the "moral" of your story is that players should err on the side of overstating their strength somewhat when having to estimate rank. This way they don't have to play games that are "not all that fun" while their rating normalizes.

I have to disagree about Tchan's reasons for sandbagging. They seem to just be rationalizations for unsportsmanlike behavior. I say this from past experience exhibiting unsportsmanlike behavior and rationalizing it.

*Edit:
If someone is really doing this once-in-a-while it's probably helpful but if it is their M.O. isn't it just sandbagging in the unsportsmanlike sense?

The best example of sandbagging can be seen in Hikaru no Go. Waya who is an insei playing as zelda on the net one day came online to sandbag, only to be sandbagged by Sai

I played a game today on IGS and was very quickly obliterated. Oddly though, once the outcome of the game was obvious even to me, my opponent forfeited. Looking at the player's rank history (below), I thought of all of the threads on this site about sandbagging. What do people think? I have no idea what this player's actual rank is but it's hard for me to see how this could occur without intentionally manipulating his rank.

I get that all of us can be slightly under ranked at various times -- playing while sick, distracted, on a mobile device, having a beer... -- but this seems extreme.

Obviously sandbagging.

Using your rating is a form of sandbagging.

What do you mean by that? And what is the connection to my >5 year old posting that you quote? Please elaborate.

Sandbagging might actually be a good way to get back in shape, or learn some new things.
As a matter of fact, the owner of a Baduk school I frequent told me to play at 5 stones below my level and work my way back up to get back in shape. I did not ask for details, and was kind of confused at first. As for me, it worked for two reasons:
1. You become more aware of your opponent's, but also your own mistakes. Thus it helped me to play more solid, for even weaker players can punish if you play loosely.
2. It helped me focus on only the game, instead of my opponent. The thought 'I have to beat this guy/girl because they're weaker then me.' can easily cost you a game. Rather, focus on what's going on on the board. Your opponent is invisible and rankless, only their moves exist at the moment of the game.

Not sure what sandbagging can help any play strength. There is handicap stones available if stronger player want to play weaker plays.

If by "back in shape" you are implying that you are not playing at the level at which you are current ranked, this just seems like accepting that your current play is below your official rank. It does not seem like you are sandbagging, but rather just acknowledging that your "true" rank is lower than your actual one. Similarly, if you are trying new strategies, you also wouldn't be playing at your normal full strength.

In the example I posted, I have a hard time believing that someone who can play as high as 1k would need or want to play at the 13 or 14k level to experiment with new ideas.