iirc ~Owls and ~OwlsTwo are the most NC recently guides for values though that doesn't mean they could not be wrong (situations on the past where users tried to manipulate values...)
That aside, from now on every DW release include the OG items on the NC Mall which will tank their value (so everyone either try to avoid trading or trading high before the value drops).
I knew there was a discord server for Owls values too.
(you need an account to see links)
The other option is making a VC (value check) thread so different users can give you a feedback.
As a gold rule if you're often confused with values, DON'T trade by neomail otherwise people can take advantage of you. Public trading is better because at least you will get advice before being scammed most of the times.
Last guide before Owls was ~Waka, though it's outdated by 1 year or a little more? Then there's ~Valisar for caps.
I've heard a bit about ~Upstairs and there's another that talks about ratios on ~eya
Not sure if there's more but I hope it helps a bit at least