I have had auctions closed early on me, and I 
have done it also.  The General thing seems to be
that unless someone is offering you a huge amount
of money, usually far beyond your reserve, that
people will consider ending the auction early.
The things to remember are that no one can leave
you a comment for anything on Ebay, except if they
are the high bidder, or the seller to the high
bidder.  Nobody else can leave feedback, so that
should not worry you.  As for the money part of it
at this point everybody should know what ebay is 
really about.  You stick your item up, and the 
longer the auction, the more exposure that it 
receives.  And then comes the last day, and every 
one who is serious about the item will come and
bid to make sure that they get the item if they
really want it.  You usually have to do some
advertising, here on the forum, on the Cels ML, 
and maybe on newsgroups,rec.arts.anime.marketplace
for example.  Stress to anybody that wants to
purchase anything before auctions end that you
really need the money, and need as much as you 
can get out of the cel.  The bad side is that
people who are bidding on an auction, and find
that it has been ended early, usually are not
happy about it, and have a tendency to remember
that you did that.  So all in all, unless the
amount is so high that is being offered, it 
usually is not worth it to end an auction early.
Hope that this helps ^_^