Granted, if I'm just selling something and not 
taking a commission, I let people know I got the 
payment and that the cel is going out the next 
morning or next day the post office is open, but 
I like talking to people.  I'm not going to be 
chatty if someone just sends me a quick 
impersonal message, but if someone asks 
questions, make comments, etc, always.  

When it comes to commissions, I'm *extremely* 
informative.  First of all, when doing fancels, 
there's all sorts of options, so I give a 
explanation of the pros and cons of each type of 
acetate/lines/paint/etc I can use.  After people 
decide on stuff, I give them updates as the cel 
goes along, send in-progress scans usually about 
every day if the cel takes me more than one day 
to do, and send them a final scan to 'approve' 
before I send anything anywhere.  And then 
there's the backgrounds choices sometimes... 
dozens of scans of the same cell against 
different backgrounds!  I also tell people to let 
me know if the cel arrives ok, because packaging 
and mean mailmen can be a problem sometimes.

Keep in mind though, I usually only have around 
three customers TOPS in any given time period for 
commissions, and I'm sure major cel dealers could 
have hundreds.  With cels getting more and more 
popular, can't really blame someone for being 
curt during a flood of orders after an update so 
that they can get everything processed faster.  
Some people prefer friendly, some people prefer 
efficiency, on both sellers and buyers sides.