I've only purchased from ECS and no experience on returns or customer service.
If I have to nitpick, my only complaints would be the couple of days delay before it ships out but I don't expect them to be Amazon-quick.

For those who expects all companies should have Amazon level of customer-service, you have to look at a few things:

1. Customer service cost money and great customer service is very expensive
2. Amazon makes a net profit of about 1%, they make money from the bulk of what they sell
3. I have to pay for prime account to have the fast 2-3 days shipping every year (I've been a member for 7, 8 years now), its totally worth it
4. Not all companies have Amazon-level of customer service (again, because of #1).

I used to own my business and having great customer service not only involves money, time, training, company culture, etc. I'm not defending ECS but I wouldn't expect them to be Amazon either. Amazon sells everything from food, clothing, and toys, car stuff, jewelry, big TVs...basically everything you can think off. What that means is, they loose money when you call them for support but they know that tomorrow, or next week, you'll be back again to buy your kid's diaper.

ECS is a totally different business. How many times do you buy a cable for your iPhone? How many times do you change your oil or upgrade something on your car? Once a year? Once in your car's lifetime? How big are they in relation to Amazon?

I'm not saying that ECS has an excuse for bad customer service but just having one of their customer guys here willing to help us is already good rep and two thumbs up in my book. I have dealt with a few forum vendors but IMO, ECS is one of the good guys out there.