I used Celga once.  I never had a problem with 
them - they're friendly people!  But, I should 
say that they are a small part-time business.  If 
you want to bid in real-time (like you would an 
eBay auction), I would suggest a different 
deputy.  If you already know your maximum price 
that you're willing to spend on the cel, Celga is 
the place for you.  They try and snipe cels at 
the last minute, so your bid won't show up until 
then (don't worry!)  Their prices are a touch 
cheaper than other deputies, but that's because 
they don't have a fancy website to keep up, or 
lots of employees to pay! ^_^ 
  The one transaction I did through them got me a 
beautiful cel, so I have no complaints.  

They're super-nice people --- if you have any 
questions, just email them and ask! :)