So, a few things to address here! 😛
Nominations and votes are handled differently. For nominations, you do not have to have an active giffgaff SIM card, as you can be a member without one. For example, if you've left giffgaff as a mobile provider but stick around for the community, you should be able to nominate. What's important is that you have a relationship with our community - you don't have to have a transactional relationship with us to do it.
We do scrutinise all nominations to make sure they're being given by established giffgaff members. We remove any accounts from the nominations who are astroturfing or not being genuine, which thankfully is very low - although it has happened, which is why we check. They don't necessarily appear from the public thread when we do this, although it may happen - and has - if we think it might shift members' perception of a charity.
One important thing to remember is the thing that was mentioned earlier in the thread - someone's registration date is not a good indicator of if they're a giffgaffer or not. Someone who has had a SIM since 2012 and only visited the community for the first time today will have the same registration date visible as someone who registered for a forum-only account today. As a non-staffer, it's much harder to tell the difference, although of course on our end we can see if someone has had an existing relationship with us and check their provenance.
In addition, the effect of the points statement is something to consider. We get a lot of traffic to the nominations thread from that email, and so it can often seem like there's something sinister going on, whereas the effect can be just because that audience tends to nominate more well-known charities. It's not just that, of course, some charities do try to tip the scales disingenuously, but for one - we're quite good at spotting when that happens, and two - it doesn't happen as much as it might seem.
When votes close, I look at the charity nominations, and do one final audit of our top five. I look at every nomination, the nominator's history, and determine whether they are legitimate or not in a number of ways - are they the same people on two accounts, for example, or are they someone who works for the charity and hasn't disclosed it, have they registered just to nominate, etc. Basically, everyone gets double-checked. If they're not legitimate and haven't been removed earlier, then they are removed at this stage. We've had the top five move around when doing this, but we've never had it be the decider for who goes up for the vote.
For votes, that's managed much more close to the chest and is a bit simpler. We send an email message directly to everyone who has Payback points in the first instance. We send it to those who don't if we have the opportunity, but typically we're only able to get out the vote to that group. Everyone has a single-use voting link that they use to vote on this site - I'm sure you've seen it before. This goes out to people who have points in the bank and are opted in to marketing. Everyone who meets those criteria gets one vote through a web app we manage, and at the deadline, whoever's got the top two slots gets allocated the donation.