I do understand the fear of retaliation thing.
When someone sends you something crappy, you don't want to give bad feedback. You know he will retaliate with negative feedback of his own, saying "BUYER WAS A JERK". When you have like 4 feedback and he has 212000+ feedback, this retaliation hurts you a whole lot more than your initial feedback hurt him. So you just don't give any, or you leave a good feedback and just never deal with him again... which makes the whole feedback system completely moot.
Yeah, when I first started out, I would leave negative feedback if I was dissatisfied with a seller...then I'd wonder how I received negative feedback in return, even if I paid promptly and was polite. This is pretty devastating for "newbies", because I wasn't able to purchase a few items on eBay because of my negative feedback score. Right now, I'm only at 75%.
I had one seller recently force me to leave good feedback before he would even give me a refund for a broken product. eBay in general is just fucking wack, and I have the worst luck with sellers because I'm always sold falsely advertised products that are clearly not in the described condition.
Sellers also seem to be overcompensating for fees and gouging on shipping prices, too...it doesn't cost 12 dollars to ship a fucking CD from New Jersey to Delaware.