Giftmoot membership and distribution
There are at least two issues that giftmoots could face with distribution: first, that someone could go from giftmoot to giftmoot and continually claim lots of resources unchecked, and second, that giftmoots could hoard resources for their members and deny them to everyone else. One of the ways to mitigate these issues is to propose some principles on giftmoot membership, which I describe below.
Before I delve into those, however, I want to express that I think it unlikely that these are genuinely pressing issues. Could a person go from giftmoot to giftmoot, claiming the maximum amount of resources that each provides without any of the giftmoots being aware of the duplicate or triplicate distribution? Yes, it is possible. But is it likely? I'm not convinced that it is. I'll give a few reasons why. The first is that people are likely to be less greedy in a giftmoot economy than an exchange economy, because goods don't have exchange value and there is no motivation to accrue as much exchange capacity as possible. The second is that because goods don't have exchange value, goods that aren't being used are a cost rather than an asset. The third is that, given it is likely far fewer people would try to "game the system", the cost of policing it thoroughly would probably be higher than doing nothing at all - though I do propose a membership principle that would provide some mitigation for minimal effort.
Could a giftmoot hoard goods for themselves and never share them with outsiders, making a luxurious community for themselves? Again, it is possible, but very unlikely. Think about a giftmoot that is going to hoard food - before they can do this, they have to convince the producers of the food to provide a sufficient amount to their giftmoot. There are, roughly, three options here. The first option is that the producers don't want to over-allocate food to one giftmoot, and don't provide with so much that there is a distinct inequality between this giftmoot and others. The second is that the giftmoot lies, saying it will distribute the food to more people than it really is, justifying the excess quantity. This would likely be difficult to sustain, given that giftmoots would be making commitments to transparency (and might be treated a bit suspiciously if not). The third is that the producers of food could be sympathetic to the hoarding motivations of the giftmoot, and are happy to allocate them excess food. This would certainly give the giftmoot excess food, but it would also only give them excess food of the type that the sympathetic producers created. So if they wanted a variety of luxuries, including, say, lobsters and salmon and ducks and cavier, they would need the sympathies of the lobster producers and the salmon producers and the duck producers, and so on. And if they also wanted mansions and fancy cars and yachts, they would also need sympathetic producers in those industries as well. And the result would be either one of two things: the entire society is eventually included, or there is some widespread cultural discourse of exclusion, which is a problem above and beyond the "merely" economic one of a group of selfish actors. Note that exchange economies have had histories (and presents) where various groups, even when they have sufficient money, are excluded from receiving goods and services. Some of those problems are solved with regulation, which is the sort of context that I present here.
Primary giftmoot membership
The first principle is that while people can be members of as many giftmoots as they like, they can only have primary membership with one giftmoot. That means that they can avail themselves of the various resources that the giftmoots they are members of can offer, their basic right to essential resources would be fulfilled at only one of those giftmoots. Those basic rights are the ones that people agree should be afforded no matter the context, while other types of distribution can be allocated based on various conditions determined by the giftmoot. So there might be a waiting list for something like a gaming computer, while food would be given out without question. People could still shop around from giftmoot to giftmoot, but while they would be guaranteed the basics, they wouldn't be able to double up.
Inclusive-distribution giftmoots
The second principle is that if a giftmoot is going to distribute goods to its members, its membership must be open to everyone. That means that a giftmoot can't restrict who it is going to distribute its goods to. If a giftmoot has a very generous policy, it will likely attract new members, and if it has a very austere policy, it will likely shed members.
Exclusive-intermediary giftmoots
The third principle is the logically complementary principle: if a giftmoot wants to have exclusive membership, it cannot distribute goods to its members. Instead, it must distribute the goods to other giftmoots.
This principle allows a giftmoot to consist of an exclusive group, such as a group of experts in a particular field, enabling them to give considered and knowledgeable reasons to distribute scarce goods (such as doctors deliberating on the allocation of medicine), or to advocate for particular needs (such as people with specific disabilities procuring relevant resources for accommodations).
With these two principles combined, an exclusive giftmoot can hoard, but not use, resources, which is likely of no use to them, and instead are likely to pass those resources onto a giftmoot with inclusive membership that can distribute goods. Even if the members of the exclusive giftmoot are also the members of the distribution giftmoot, they cannot guarantee that they will remain the only members because that membership must be open. So a giftmoot that gains an excess of resources cannot make a generous allocation principle just for themselves, and a very generous allocation principle is likely to draw in other members as well.