Possible Large collection purchase (How to Approach)

[Ironheart]

I have a lead on a potential large collection that is up for sale. It has supposedly never been picked through and is untouched. Close to 600,000+ cards

The seller claims that is all came from Ontario from his grandfathers coin and collectible shop. It is primarily hockey, baseball and all other sports. Supposedly there is dealer special release autographs, promo items and high demand rookies (his words) not my interpretations of what he claims. Years is ranging from the 1960's up until 2007-2008. He is asking $8000 but says no reasonable offer would be refused. The stacks are roughly 11 high and 4 wide and supposedly the stacks are 2 or 3 deep

My interpretation, is there may some valuable rookie and vintage cards are possibly there, however he may basing it off of sheer volume at roughly $100 a box if there is 88 of them.

Would any of you personally take on this amount of cards or would this be a very quick pass. I would have a place to put them, but the amount is shocking to break them down for resale and just keep the good stuff. I'll be seeing it on the weekend and probably taking 2-3 hours to look through it all.

How do you approach a collection like this and making an offer.
Thanks in advance.