Help with selling item please?

[GMCjunkie]

This is not a post to sell somthing, I need help with how to go about it please. Ive removed the AMA aftermarket under dash A/C unit from my Burb. I bought it in 2002, and paid 750.00 for the unit. It was used very very rarely. Im restoring the inside of my burb now,and I just do not like the looks of it any more, and as I said, I never use it. Ok, this sounds cliche' but, "It worked 3 years ago when I took it out of my burb to put it in the paint shop" I have not hooked it up to see if it works since. My question is how should I list this for sale on the parts board? How much would it be worth? Having not had it actually running in the last 3 years, how should I offer some kind of guarantee, in case it dosent work? I dont want to sell it to someone and it not work, but I dont want to sell it and them not try to install in for a year, after having let it sit in the back of an old truck in the weather in that year, am I making sense? Its early and Im only on my second cup of joe. If you need more info to help me, please ask.
Thanks everyone!

junk