Hello there! I was reading through your blog, and this post inspired me to wax a little bit! Sorry for a six-month-old reply!
People have their own opinions and convictions, and if it were easy to sway people's minds through genuine information, there would be a lot fewer creationists, et al, on this planet.
The thing is, human beings need a sense of superiority and/or control. This isn't necessarily a bad thing, and is a tendency that's present in almost every person. When people are deprived of this sense, we feel insecurity or emasculation. Most people experience these feelings during their adolescence, in the process through which they eventually form their adult identity. A sense of control is generally established in either of two ways. The first, more common method is to simply maintain one's beliefs and not tolerate/listen to criticism regarding oneself or one's decisions. The second is to acknowledge the fact that perfection is impossible and that some criticisms about oneself are valid. In this case, a person will remain open to criticism, taking what others see as insults as opportunities to improve themselves and allowing one's identity to possible change over time as they work to fix their own flaws.The second path is especially difficult, simply because it's painful for a person to admit that they are flawed and will never achieve perfection.
So what does all of this have to do with the topic?
When you provide advice, LFF, you are asking the person you're talking to to allow your judgement to decide an aspect of their life for them. In essence, you're asking them to relax their control over the situation. In this case, most people, seeing you as a stranger, will give you no mind at all, because to accept your advice would mean to admit that you are a better judge of headphones for them than they themselves are. This may not be the point you are insinuating, but that is what the subconscious mind takes it as, especially since you are a stranger to the person(s) being advised.
I have personally found that the best way to give advice that will be followed, or even to convince most people to do anything, is to attempt to get your subject to reach the same conclusion you did via their own thought process. People instinctively recoil at things that are foreign. Ideas are no exception. Conversely, human beings automatically give more value to their own ideas. You can use this to your advantage; by having the person you are advising follow your thought process and arrive at the same conclusion you did. That way, you don't suddenly confront them with a foreign new idea ("Buy this. It's the best choice."), avoid making them feel insecure ("Those headphones that you chose are junk. These ones are better."), and allow them to reach your conclusion themselves, thus making it "their idea" and giving it more value in their head.
So how do you do this?
A person is looking for headphones. He picks up some Dr. Dre Studios. Cue Toccata and Fugue in D minor.
First of all, (obviously,) don't just butt in and start offering advice. If they didn't ask for help, there's not much you can do by force-feeding it to them. Obviously, you already know this, but I had to include it for completeness.
So he says aloud, "I wonder if these are really worth the money"
It's tempting to reply with a slick "They're not," but it would be much more effective if you were to say something like:
"Oh! Yeah! You know, most real DJs actually avoid Beats like the plague."
You could even stick an "I heard" in there to make yourself sound more unsure -- If you want a stranger to follow your advice, it's usually more helpful to appear to be closer to their knowledge level than to show off your awesome understanding of sound (which they won't really trust anyway, because there are no such things as "audiophile credentials." A shame, really). Anyway, let's continue:
"Yeah. Apparently, they break a whole lot, and you can get a lot nicer sound for the price if you're not paying for the Dr. Dre designer label."
Now we've given the guy some reasons that make sense to him about why Beats might not be the best choice. Let's see what happens when he responds with some justification:
"But-but Dr. Dre uses them! He's a professional and everything!"
"Well, Dr. Dre actually uses the Beats Pro, which are $500 headphones. They're made of metal, and people say they're okay studio headphones, but they're too heavy to use for listening to music and stuff. They sound a lot better than the plastic Beats."
At this point, we've finally pulled the "Beats suck" card, but we've given our subject a scapegoat! It's no longer "This guy's criticizing my decision to buy Beats," but "Dre's pulling the wool over our eyes with his fancy schmancy metal headphones!" Now, you can go ahead and show him some nicer cans, and he can make an informed decision. He may pick the Beats -- some people truly are intractable -- but at this point, you've provided your advice, and done so in a way such that he can't dismiss your information for being critical.
I hope that helped. I look forward to a reply.