Are they working for you without a problem? If yes, then they are in a good condition! I would expect zero questions on eBay from your buyers. You list it, say a few words, and wait a week for it to sell.
I sell quite a lot of my used stuff on eBay. It's an incredible tool to reduce the cost of your equipment. I easily get 25% to 50% back from my purchase price when I upgrade every few years.
My favorite sale of all time was when I sold a broken PS3 for parts for $100 (and there were 10+ different unique bidders over the course of the week)!!
Sandy Bridge and newer CPUs in particular right now are holding their value really well. You can check closed listings for what stuff has sold for recently. For example, right now I am using i7-2600k that I bough in 2011 (and it's doing fantastic and I don't plan on upgrading right now etc. etc.). At the time I paid $319 for it. Looking at closed auction listings on eBay shows that it's an incredibly popular item that sells for $160 to $200. 50% to 60% back on a 4-year old CPU is amazing.
The high resale value speaks to the parts' long-term reliability, even when you know that what you are buying may have been overclocked, etc. The other cause is the relatively slow rate of performance improvement compared to prior years. Overclocked i7-2600k will still perform on par with a brand new stock core i7-6700k.
The bottom line is, selling is easy, there is a ton of money in it, and you don't need to do anything complicated to do it.