if I was the seller, and someone had offered 
let's say $200 for a cel months ago, then someone 
else offers $600, I wouldn't feel obligated to 
send a heads up to the first email unless it was 
a collector friend of mine. besides, what are the 
chances that someone will counter offer 3x the 
amount they first offered? just a devil's 
advocate point of view.
   I've been very successful with offers, about 
one in 5 will have positive results. I also take 
the rejections well and move on. I think this is 
the trick to staying sane, if you can't take 
rejection, you shouldn't make the offers. 

/mina