Quite often a game will be very close, from a few points to half a point.
Sometimes when I am the one behind and I fill in the dame I can turn the result to a win for me by half a point or one or two points.
Frequently I feel a little bad winning this way, what do others think?
Having said that, one recent game the score estimate indicated that I had won by a point or so (no dames filled). I thanked my opponent and passed to end the game only to find my opponent started to fill the dames. Fortunately I won the dame fight!
If you want to make sure,… just be upfront about Chinese rules and mention it at the start and before yose.
The OGS game offer window shows which ruleset is used, but a) it’s at the end, so mobile users won’t see it, b) nobody expects it and c) to find out when you’re in the game, you’d have to navigate to “game info” via the s(l)ide menu.
Alternatively, you can just use Japanese rules.
If you are using chinese rules and your opponent doesn’t play the dames, it’s his/her own fault to give you free points.
If youa re using japanese rules, and your damefilling forces your opponent to play into his/her territory, it’s called teire, and it would be your mistake to let your opponent to count those as points.
The score estimator uses always area scoring. It counts all marked points for the respective player.
Depending on the actual rule set (area/territory scoring, how seki is scored, …) the estimation can differ from the correct result even if the game is completed and live/dead groups are correctly identified.
If the game is close you should count yourself and not rely on the SE (it is likely wrong by 1 or 2 points because the different scoring methods)
About filling dame:
If you use a rule set with territory scoring, filling dame is worth 0 points. So it is not necessary to fill all dame
Under area scoring (chinese, aga, …) filling dame is worth 1 point.
Well, you can’t blame yourself for your opponent’s blunder, assuming that you are talking about your opponent overlooking a preventable teire.
I took a look at some of your games and they all seemed to be under Japanese rules, so maybe it really is just the misunderstanding about the score estimator? Under Japanese rules filling (real) dame does absolutely nothing and it could not have been the reason for a victory (it can change the score estimate, but not the result) so no reason to feel bad at all.
If you really mean filling dame under Chinese rules when the opponent did not notice the ruleset… Well it is nothing to feel bad about, your opponent should have checked, but at the same time I would not feel good about such a win either.
Dame filling is important in Japanese rules. As @_KoBa mentioned, filling dame can compel your opponent to play moves within their own territory, which affects the score (teire).
Technically, under Japanese rules, fill-able dames should be played in order to properly determine whether or not stones are alive in seki. Determining whether stones are in seki is important, since Japanese rules does not count “eyes in seki” as territory. Here are the relevant rules:
From Article 8 of the Translated Japanese Rules
Empty points surrounded by the live stones of just one player are called “eye points.” Other empty points are called “dame.” Stones which are alive but possess dame are said to be in “seki.” Eye points surrounded by stones that are alive but not in seki are called “territory,” each eye point counting as one point of territory.
Thus, if dame are not filled, one could claim that the adjacent stones are only alive in seki and that there eye points do not count as territory. Of course, that’s not what actually happens in practice with reasonable players, but I think the rules are there for particularly tricky life/death/seki situations.