Feedback: Useful tool or dangerous weapon?

I'm interested in hearing people's feedback (heh - see what I did there?) about feedback. Do you ever leave negative feedback on places like Etsy, eBay, BPAL forum, etc? What would induce you to to do so? Would you attempt to discuss your issue with the seller first?

The reason I ask is that there have been a couple of times (luckily, not very many) where I have been tempted to leave - if not bad feedback, then at least neutral, but I haven't done so because I've heard so many internet horror stories of vengeful sellers stalking people and harassing them, or nasty buyers conducting a campaign against a seller because of one bad incident. I like to Keep Things Noice, so when I'm not overly happy with a purchase or a purchasing experience I tend to just shut up and not buy from there again. For example:


1. Some products I bought from an Etsy seller took AGES to get to me - over a month. Now, if there were something on their page saying that their products usually take 2-3 weeks to ship (they may have been making them individually for each order or something), then fine. Or if there were some delay due to life getting in the way and they either posted a notice to that effect or emailed their customers, or even included a short apology note in the package, then fine. But I heard nothing. Now, I already had my back up because this particular seller had ridiculously high shipping costs compared to anyone else I'd bought similar items from, so the delay just peeved me even more. When the products finally turned up, I didn't like them. In fact, I really hated them. The scents smelled cheap - like the kind of perfume oils you'd buy in The Reject Shop, and there was a lip balm that was actually really good quality but SO overscented that directly under one's nose it smelled like vomit (Noodles agreed with this assessment). But I still left mildly good feedback because:

• Maybe they were ill and that delayed the sending, I don't know. Most of their feedback was along the lines of praising fast shipping, so I thought it must have been an anomaly. 
• The postage cost - while annoying - wasn't worth getting strung out over, to me anyway.
• The like or dislike of a scent is a personal opinion, and I don't know that I should be giving bad feedback based on that. 

2. This one actually really annoyed me, and is probably why I am writing this post - I'm still kind of stewing on it a couple of months later. I bought Noodle Arms a headband she wanted from an Etsy seller. It was $16.50USD, a ridiculous price for a cheap little metal headband with plastic flower, but Noodles loved it and I was feeling generous, so what the hell, right? When it came it was broken. It wasn't particularly well packaged - loosely wrapped in plastic and in a bubble wrap envelope. Nonetheless, I am not one to create drama out of minor issues, so I wrote to the seller to explain the problem and ask what kind of glue I should use to fix it. So you see - not demanding a replacement, and willing to cough up the five or six bucks on top of an already overpriced product to fix the damn thing. She writes back immediately saying something like, "Oh, I can't believe Australia Post - they're so terrible blah blah blah after I wrapped it up snug and tight and everything!" Well, no - she didn't. But never mind. She told me what glue to use and I went and bought some (but don't you think it would have been nice if she'd offered to have me send it back and fix it for me or something? She's Australian, so it would have only been a day or so post each way). I fixed it and a week later it broke again. It sat on the kitchen bench for a few weeks until Noodles super-glued the plastic flower to a hair pin and made herself a cute little hair clip. She was happy, I was out $16.50USD plus postage plus the cost of glue to fix the damn thing in the first place. Needless to say I was not happy.

I didn't leave bad feedback on that second one either, but I wish I had. I thought the fact that she immediately abrogated herself of responsibility (Oh, damn Australia Post!) was crappy - what the hell did she think I was going to do? Sue her? I also thought the fact that she didn't offer to fix or replace it was a bit rubbish as well, though admittedly I didn't ask. (It's not that I minded fixing it myself at first, but she could have offered, you know?).

So... I don't know. Where's the line between petty whinging and a legitimate grievance? I don't ever want to be one of those people who drives e-tailers mad with constant complaints and higher than reasonable expectations, and I don't want to get retaliatory bad feedback after being honest with someone either (I have the same username pretty much everywhere I shop so that could have ramifications of its own).

What do you think about the whole issue of feedback?