as a buyer, i really dont touch ebay unless theres something i really want, or a bargin (like mechano dockside locos at £7 a pop) its to much of a pain and things are often over priced/gets silly, ive often been outbid on an item for it to sell for more then what it costs brand new!
as a seller, i do quite well, i often sell alot of stuff for a friend whos thinning his collection (hes been a collector for years, and has almost every scale in CN and a number of american roads) i tend to post items the next day after i get payment, if they take a few days to pay, i'll wait a few days to pay, i dont drive and i walk the 4 mile round trip to the post office, i reuse packing and charge at cost/touch more for packing and the effort to post the item/s smaller items always go 2nd class recorded, and larger items by whatever is cheapest, this seams to keep the buyers happy as i have 100% feedback (apart from one muppet who "pushed the wrong button" on his iphone and never changed it, got it sorted when i got in touch with ebay about this matter.
i also have a habbit of buying cheap crap from shows and selling it on ebay, everything is honest, i dont buy locos/stock unless its dirt cheap (like carboot sale cheap) i normal pick some stuff out those 10p bags and stick them on ebay, will often get at least £5 for something like old triang stuff, loco plates, crap figures etc.
from time to time i put an add in the paper and get a box of stuff people dont want for a tenner, sort it out, junk whats worthless and sell the rest. so far the biggest "win" was a non running Hornby 0-4-0 cheapo saddle tank loco, listed as non running twice, brought for £3 at car boot, sold for just over £30, ive also picked up brand new Hornby decoders from local shops/hattons stick them on ebay with a 99p start and they always end for a few quid more, upto £5 more.
you could say its unfair, but im only doing what ever 2nd hand trader dose, buy cheap, sell for profit, if someone wants to pay money for something, im not stupid enough to refuse.