I hear what you're saying, but I don't know if that's right. The rewards are fixed, and hence zero sum I think? If everyone contributes 50 FPs, and you swoop in and put in 80 to win 100 let's say, did you really help? The GB owner saved 80 FPs, you net 20 FPs, and the other contributors collectively lost 100 FPs.
If your arc is higher than the ones you overtake, it isn't a 0 sum game but a positive sum one.
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My guild clearly states that you can snipe and be sniped in the GBs of your guildmates, and I think that's the best. If they always are in an overprotective environment they will never learn. This way people will (hopefully) learn when and how to lock their spots. They will learn how not to be sniped hundreds of FPs by an enemy guild.
I'll put a real example.
Through guild swap threads I was 1st in a lvl ~20 arc (I think I didn't have an arc at the time, I would have locked the position if so). A guildmate with lvl 60 or so said he could snipe it but he wasn't going to do it out of respect for me. I told him that this was a mistake, and he should do it. Then, the guy who was 2nd complained and in the end, my guildmate didn't snipe. The following day the GB received more donations, and was (obviously) sniped at a much larger benefit from a neighbour. For me, this is not courtesy, it is idiocity
Result:
The guildmate with high arc lost a snipping oportunity.
The guild mate owner of the GB got sniped by an outsider and received less FP.
I stayed more or less the same.
The guy who was 2nd traded a few more FPs thinking it would make a difference, but the only thing he did was increasing the sniper's benefits.
This is not to say we snipe everything on sight. There are a few people that have deals among themselves (anyone who checks GBs regularly would notice). They know how to keep the rewards within the group, but there is one person who keeps messing up and puts FP when he shouldn't.
I've messaged them and we have come to an agreement: if it can be sniped but for low value I message them and give them a few hours to fix it until I snipe; if they mess up big time I snipe it on sight. And I know there are other high arc players in my guild who do similar things.