Love ebay, as a buyer...haven't tried selling, yet. The auctions are fun, if the wait is a bit frustrating at times. I've only had one bad seller there, all others have been great, especially when it comes to answering questions.
As in all online sites you have to check on the seller reliability, that's what burned me when I first started buying...make to sure to check customer comments for each seller I buy from...Though this can be unreliable when it comes to the Chinese sellers. Personally, I don't buy from anyone with a rating below 99.0% rating and have only been burned once.
Paying with Paypal has been great as I don't have to give any credit card info to each individual seller when making purchases. Hopefully I will still have this option when ebay and Paypal split. I've gone on to use Paypal when shopping other sites, keeping all of my credit card info private and in one place rather than spread out across the internet. You don't have to have a Paypal card to use Paypal...
As far as Customer Service goes, The only problems I've had was in language and I requested, nicely, to have another representative with better English and everything was settled. I have always been treated with respect and my problems resolved within one phone call (*******229, 5AM - 10PM PT, M-Sun).
UPDATE: Just last month, Jan 2016, I was burned on a purchase from China. The seller expected to get favorable rating for item when 2 cords were missing. This is NOT ebay's fault but the seller. I got burned because I compromised on the 99% feedback rule I usually follow...this seller had 99.4%.
After reading some of the complaints I realized that many, not all, are blaming ebay alone for the sellers' ripping people off. If buyers do their homework...check feedback and do Searches online for customer reviews of brands, there's less chance of being taken. Don't want to say ebay is perfect and always gets buyer's money returned, but it's ultimately up to the buyer for refunds. Too many complaints against a seller then ebay suspends them... Not sure how that works since not seller. Do remember that after the 30 days nothing will be done...you have contact the seller yourself....Been there, Done that and it doesn't work, at least for me.