The only deals I've ever seen from Ecost were really good... until they canceled them. And then tried to fuck some people over by charging about twice what they were originally asking and keeping the money held in everyone's accounts for about 2 weeks. This experience was about a year ago, so maybe they changed, but I'd steer clear if I were you.
I've bought from them in the past and just recently. Got a refurbished Onkyo stereo receiver and a refurbished Sony CD player. Shipped promptly and worked fine. I've never experienced overcharges on good deals or suspicious cancellations. Not to say it doesn't happen, but I've had many orders never had a problem. I can't say anything about customer service because I've never needed it.