Chris is very easy to get in touch with if you're serious about a machine or want to authenticate the game you're looking at..But even he may not always be able to tell you what a used one should be worth today.. it all depends really on what the original buyer paid for his used game and when Chris did the restore.. AND look on his web page... it's pretty well mapped out what it will cost you TODAY to start/complete a basic Williams type restoration.. variations depending on parts needed...

A person may have sent him a game a few years ago that was trashed and had from a barn for $500 and then had it restored for less than today (read his postings.. and view the pics.. he almost alway does a complete new cabinet nowadays)....

Read his weppage..
Read his history here...
https://pinside.com/pinball/forum/topic/the-evolution-of-hephigh-end-pins

Chat with the seller first and find out more about the game.. original condition, year purchased, and what all done by HEP and you'll get a ball park idea on what you should be offering..

Actually, yeah I think you will.. I know he brands the pf on a full restore.. does he not do the same on the bottom of the pf for just pf restoration?