In the past, I have bought out collections from collectors, usually by word of mouth. Besides the time, I have found that with what I have paid, this approach is generally fairly profitable.
However, some of the quickest money I have ever made is by reviewing collections and connecting the collector to an AH that would best serve their needs. A recent referral I made netted the collector nearly $30k for their collection and they paid me $500 for my time to review the collection (an hour or so), provide my recommendation on selling and reaching out initially to an AH. From a time standpoint, the several times I have made an AH referral to a collector, this has been my best use of my time for the money. In other words, being the middleman is more profitable than being the end seller.
If you have seen the you tube channel "Chasing Cardboard"
https://www.youtube.com/@CHASINGCARDBOARD/videos , you will see Ty has taken multiple approaches to handling the sales of purchased collections. As he has evolved, you can see that he is now more likely to make a referral/help consign a collection than to rent a storge unit for a collection purchase.
So, while buying a collection is far more exciting, reviewing a collection and making a referral is much more profitable based on time spent/money earned.