I have bought more collections than I can think of ranging from 500 to 5000 books. I had a guy similar to what you are describing and I was only a three hour drive and I like to hunt so I lined up some other spots to hit on the way. Most of the collection was not bag and board and I definitely had a WTH look when it was one long box and 20 shoe boxes. The guy however did have them in bags. He must have moved those shoe boxes very carefully because most of the collection was flawless. He wanted $1000 and I told him that I could only do 35 cent a book unless he had something special. I made sure while negotiating to bring up 200 books were 90's image. (If anyone needs a Brigade, Youngbloods, Shadowhawk, or Savage Dragon, I'm the man) Pointed out the 50 Punisher War Zone #1s and 40 Wolverine #50. He was reluctant so I started going through all these 90's comics that were the last thing I wanted to see and then I saw his 90's ASM run. Just like the Punishers and Wolverines the guy bought multiple of books he thought would be something and I saw the 10 ASM 361's. He had ASM 315-400 all 9.4-9.8. He didn't have any silvers so we settled on $700 or I was going to have to go through the whole collection. I sold 9 of the 361's for $70 and had one graded for a nice 9.8. I've made at least 8000 so far and I'm currently waiting on the keys from his entire SSv3 run to be slabbed.
You never know what you will find. That's the thrill of the hunt.
My rule is to always go in knowing the price discussed is not the final price and find enough books to hit my price. Everything else is more money in the bank!!!!!