They're not to be in it for personal gain. Now obviously you're not normally going to find someone standing for vestry because they're eager for gain. Though I guess it wouldn't hurt to check on the motives of the treasurer before you appoint one. But I think we're pretty safe at the moment. But strange as it may seem, it is possible for clergy to be interested in financial gain, even on our salaries.
Clergy can be just as greedy for money as the rest.
There have been plenty of cases where clergy have dipped their hand in the plate or have organised their own little discretionary account that no-one knows about so they can indulge themselves a little. In fact they've probably used their low salary as a justification. They shouldn't lord it over those entrusted to them, but should lead by example. In the New Testament context, a shepherd walked out in front of the sheep and the sheep followed along behind. That's what Peter has in mind here.