Thanks for all the responses everyone.
One minor correction, it was VNEA rather than APA, these were the finals in Quebec.
I was surprised actually to see fewer people take the hardline "rules are rules" stance. I was the guy telling all my teammates to stop bítching at the other team (esp. once the ref's made a ruling), and I thought it was pointless to call them unsportsmanlike. But maybe that's exactly what was called for. The losing teammate took it too far though, he kind of gets into conflict all the time even though he's a nice guy, and the girl who lost eventually got sick of the abuse and flipped him off, which led to even more abuse. I actually found that pretty funny but I'm not sure if anyone else did.
The ref asked if the other player had seen the pocket get marked and I believe she said yes. But apparently it didn't matter. Or I mis-heard and they claimed they didn't, which would be a lie. I'm not sure if the situation is mentioned in 'ref school' and there's a clearcut way it's supposed to be handled, or if it was sort of a new situation and had to be decided with a judgment call. I have never seen someone try to claim a pocket they didn't intend, though there are certainly situations where it could come up (the players hits a ball for an un-called safe, and it banks straight into the side like it had eyes, and he has shape on another ball. A lot of people would be tempted to claim it and keep shooting). But for the 8, it should just be sufficient to call and point to the pocket. If the opponent is at all unclear about it, they simply ask before you shoot. If there's debate after, 8-10 witnesses is enough to clear it up.
Many teams (including this one, I think) were ok with just calling it in earlier matches =/
Ironically I think we let some slide for them too. One guy I was playing played the 8 in an obvious corner. The marker was already sitting nearby (but not very close to the pocket, more like just past the middle diamond of the footrail). I said something like "I don't think you marked that corner but it's cool, I know what you were going for." He told me he actually was ok because the marker just has to be somewhere between the center diamond and the intended pocket. I was half tempted to mention that, if memory serves, you can't let the marker sit there from some previous shot, you must pick it up and put it back into that area. But I could be wrong on that one and anyway I wasn't gonna take it from him. He made a 3-railer to get that shot on the 8
My feeling is you abide by what the ref says and shut your mouth at that point. You won't get a reversal by continuing to grumble or berate the opposing team. The only thing you could accomplish, in theory, is to make them feel bad. I don't think that's worth doing. If they were capable of feeling bad about it then they'd just let it slide in the first place.