I have 95% positive experience with e-bay, 3% negative on the fees, and 2% negative on flaky "buyers".
Selling:
(I've sold nearly 300 items)
I have a perfect score as a seller, mainly because I take extra care to thoroughly describe every aspect of every bike, component, and part that I sell. I also take a good array of photos (especially of bikes), in good light, to show great detail, and point out every defect so that I can't be faulted for not describing or mentioning a defect. Lately I've been starting the bidding at my "bottom dollar", with no reserve; that has produced good multi-bidding sales which typically results in near the highest price the market will bear. I also spell out in the listing that the starting bid IS MY LOWEST PRICE; that has resulted in zero e-mails asking what's the lowest I'll take or the very stupid (but common) "what's your reserve?"
I've had very good results with buyers, 95% of them leave me a positive feedback, 5% leave no feedback. I've had 2 buyers "win" the item, only to flake out and not pay up. 1 time I offered an item to the next highest bidder and it sold, the other time, the flake was an only bidder.
I had one negative experience with a buyer that claimed he never received the item (an old computer), but I received the delivery notification from USPS, and supplied it to e-bay who quickly closed the case in my favor.
Shipping:
On any item that will fit in a USPS flat rate box, I include "free" shipping, and adjust my starting price to cover the flat rate box/envelope. On small items, I use USPS rate. On anything over 14", and heavy items that won't fit in flat rate boxes, I use FedEx ground / home delivery. If you buy the postage on e-bay, you get an even better discount than the typical online pricing (with account) of FedEx and USPS. I don't use UPS only because the nearest drop station is 8 miles away.
For most of my bike auctions, I include door-to-door shipping, or $500 credit towards overseas / international shipping. I use Keyboard and J.C.Motors, depending on the zone (Keyboard has limited west coast service). I offer tear-down and/or crating FOR A FEE. I also offer "personal" delivery up to 400 miles away for the same cost as Keybd/JCM. I live less than 400 miles from the nearest sea port (Galveston), so that helps international buyers.
Buying:
(I've bought over 100 items, and have only 1 negative feedback as a buyer on the VERY FIRST ITEM I ever tried to buy on e-bay many years ago)
I use EZ-Sniper for auctions, and typically "Buy It Now" feature if available. EZ-Sniper has helped me win 99% of items I bid on. The 1% that I lost ended up going for way out of my price range, so no loss.
I've personally had very good success and no issues with sellers apart from one very flaky seller that took almost 2 weeks to FINALLY ship my item after many excuses (I left him a "neutral" feedback score). I've only had one bad experience with a damaged part, and also left that seller a "neutral" score.
I've never had a shipping problem with any item bought on e-bay (that I can recall).
So, overall, positive experience by far.
For what it's worth, I ALWAYS offer bikes and parts here in the "For Sale" section to any member at "any reasonable offer around my starting bid".