Again, the topic was etiquette, which means what 
is acceptable, not what is possible.
I think if an item is on auction, it should be 
sold according to the terms of the auction, 
unless there is a good reason not to.  For 
example, in the case of cels, sometimes a trade 
will become part of the deal which straight 
bidding will not take into account.  Or maybe the 
seller gets a really great offer and needs money 
right away. Or perhaps there is something about 
the high bidder the seller dislikes- history of 
bad feedback, sniper, something like that- and 
the seller doesn't want to sell to him. But in 
general, I agree- set starting bid or reserve, 
then leave it alone.