A dealer would pay millions for a collection if it was worth multiple millions. But also remember that bulk purchases come with bulk discounts.

I used to sell Beatles records. If someone offered a bunch of low-value records with a total retail value of $3000, we might offer only $1000 or $1500. If someone offered a single record worth $3000, we might offer $2200. The key is how much we can mark it up, and how much effort we have to put into its resale. A bunch of low-value items might take forever to sell, so we don't want to have our investment money tied up in long-term inventory. A single high-value item might sell rather quickly - we can make our profit (even if it isn't a 100% markup), and reinvest in the next acquisition.