The concern arose from the fact that under the current system, fraudulent membership is possible - there are no effective safeguards.
I think the concern is not one or two fake memberships but more that someone could successfully do this to such a scale that they could influence a vote, either electing new trustees or passing an undesirable motion. In reality, I think the risk here is very low as long as we have a sizeable, engaged membership and sufficient candidates for board elections.
Looking back at motions and elections over the last four years I can see scant evidence that this has ever happened - in fact the only time I am aware is the very first election back in 2008, when a 16 year old tried to stand for the board and then he unsuccessfully tried again using a sockpuppet. It didn't take long for it to be exposed and it lead nowhere.
I don't agree that there are no effective safeguards against this, in particular:
- the board considers each membership application individually before approving
- the board has the power to remove people as members if necessary
That's very important - you are able to do something about it if you identify that it is happening.
For me, the key thing is keeping an open eye when you see new membership applications and spot any patterns emerging. You might want to check for multiple members with the same email address or at the same postal address or lots of people joining up just before an AGM all in the same area.
I think that would deal with the risk adequately. Credit checking, besides the costs, would require consent and can damage their credit rating so I would strongly advise against that. I would not strongly object to having confirmation cards in the post but it would seem a bit overkill and not entirely consistent with a Wikimedia culture that is predominantly online and still, for instance, allows pseudonymous admins on the English Wikipedia.
Hope this helps and hope your recruitment is a success in reversing the trend of declining membership (although I suspect this is simply because we are finally getting round to knocking long-lapsed people off the list).