A lot of unrealized systems out there...

Jmcgrogan2 is right. Things are not always what they seem. In most cases, the talk about unrealized systems is used to get the most money for whatever component is for sale. The seller probably listened to the component and didn't like it. If he's honest, and put that reason in the ad, the buyer may be turned off. Who wants to buy a component from someone who didn't like it? If they say its part of a unrealized system, they avoid putting negative comments in the add. Also, if the component is in like new condition, they may be able to sell it as new, or close to it. Who wants to buy something with a lot of hours on it?

I would say that that most are probably legit here. Feedback is your best friend.

Just because someone has good feedback doesn't mean they're reasons for selling a piece of audio equipment are legit. If you don't list a reason why you are selling, that's the first thing someone will ask.

"I'm selling this preamp because it sounds like crap. I'm sure it will sound OK for you, though. The magazine gave it a good review."

"Just because someone has good feedback doesn't mean they're reasons for selling a piece of audio equipment are legit"

Not always, but it's a good indication. And for me, works more times than not.
I see you have no feedback here. I can tell you with certainty that keeping good feedback is not easy.
I've bought many phono cartridges advertised with less than 50 hours and a couple with around 10 hours. I couldn't tell the difference from new. Bought a Condrad Johnson PV4 advertised as NOS, and it looked it.
As for listing why someone is selling an item, I couldn't care less. If you told me you didn't like the way it sounded, so what. How do I know you are an experienced listener or that you room is set up right. Maybe you have the wrong associated equipment with it.

What difference does it make why someone is selling an item? There's a small range of answers and an unscrupulous person will lie about it anyway.