Question regarding selling and pricing older equipment

So I have some older Quad 12l active bookshelf speakers that I bought on here a while back. Like 6 or 7 years ago. 

They've been great but I'm looking to swap them out for something else, and this leads me to my question: 

Obviously I could just go and look at what other 12l's are being priced at, but I'm curious about generally how you should price speakers based on the msrp vs. what their perceived value is? Is there a general rule of thumb to keep in mind, especially when selling through this type of forum? 
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take care of Hifi shark. Although its a great source if obtaining good deals, 30% is scam so prices there not very good to get a comparison. 
if you got Facebook , there is a good Group called Quad-Hifi and people there will help you by experience.

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viridian, of couse Hifi Shark it simply lists of items audio selling on other sites. I like it and i personally use it for my Preowned item as it crawls my website. All I am saying is that many frauds can come from there, listed in one place.