I think $4000 is about $1000 too high for a 2014, especially as the riding season is over in most of the USA. My 2017 was bought new, unsold, in 2019 and the out-the-door price as $4,982. It now has almost 13K trouble-free miles.
I've put another $1,500 into it in suspension, Russell "Day Long" seat and taller, wider bars, a 17T countershaft sprocket to lower revs 13% at any speed, a Scottoiler for chain lubrication and other niceties. I have owned many bikes (87) and would not have invested this heavily if I assessed the CB-500F as a less-than thoroughly well-made bike with a bulletproof engine and running gear, if given reasonable care. I also average over 70 mpg (US) consistently. (I'm old--I ride moderately.)
You didn't mention what model of Royal Enfield you've also considered. By and large, the latest iterations of Royal Enfields are vastly superior to the models of only 8-10 years ago. My 2021 Interceptor 650 has been excellent through 4,500 miles and averages 65 mpg. It is taller and heavier than the CB-500s and suspension and seating are terrible. But, the MSRP is quite low (mine was $6824 two years ago and it, too, has had the suspension seen to by IKON and YSS and the seat also is a Russell "Day Long" seat.
If the 2014 CB-500 shows no cosmetic damage and has relative low miles (less than, say, 20K--it IS 9 model years old) then work on $3000. If it does not show good care--walk away from it but keep watching Craigslist for the next 2 months. It's a great time to be shopping.
Ralph