As far as the hood is concerned, if someone has a GB that I can snipe, I see it as fair game. It is up to the GB owner to make sure the spots are locked so investors do not lose out. If they do not do this then tough. If these investors do lose out because the owner has not taken the proper steps then it is up to that owner to make good their losses. They can demand 1.9 only on their profile until the cows come home. There is no game requirement for that.
With friends I will leave their GB with one to go so they do not lose the DD. Or if it is obvious the GB is being levelled 1.9 I will stick to that as long as the spot I take is prepped for it. However I do also have friends who are quite happy to get snipers to level up their GBs. So I will take a profitable spot on their GBs.
On guild swap threads with a stated amount, the correct thing to do is stick to that amount. If you want to add more to a certain GB, then the polite thing to do is get in touch with the GB owner and arrange a private swap with them for a regular given amount on their GB and one of yours. That way you are not sniping your guild members.
If I have someone who attacks and plunders me, I will put 1 fp on any of their high level GBs that pay out FPs and keep an eye on them. Because even after the hood changes you can still add one or 2 more when that GB is close to flipping. As that way you cheat them out of the DD.