Buying Coins From A Collector

Like just carl said

I would have to know what coins he had, and in what grade he thinks.
One so I know about how much money the sale could be.
Also if you knew he had... say a 1921 D mercury in VF range. You could compare the guide you end up using, to similar coins on E bay or local shops.

I think the way he is trying to sell his coins, it might not be a good deal unless it was for coins that you want/need and in the right grade for you.

He may had been to a coin shop to sell his coins and was really low balled on a price.

Also if the coins are a lot of low grade common coins, then this is a bad way to buy coins.
For example: Look up the price of some common 1950's wheat's cents, 20% back of any guide, would be a very high price to pay for coins that trade bulk in coin shops for Two Cents each.

I think the Grey sheet value is a buch better representation of what the coin is actually worth. Those magazines have some nice articles and dealers love them because it makes their high prices seem more reasonable.

This somewhat says the imnportance of a coin dealer, saves one the effort, risk and buying coins unseen that was graded by someone else and unslabbed.

always best to buy coins seen in detail, in a safe environment and ideally in hand. that's usually the coin store

with unusual locations for buying, there is always a big chance of high margin profit, also high risk of a scam

I'd stick with coin dealers where I can see & handle the coins