It is very depressing to see large public and non profit institutions be snowed in by his showmanship and spending millions of their funds on this glorified celebrity worship. It is good for museums to have letters of famous writers and their notes and such but it is an absolute waste for them to pay millions when they can pay hundreds of thousands. For most of these archives it seems that most and all bidders would be public or non profit institutions. Why would they outbid each other to waste more public or non profit money? In many cases it seems like there was no competitive bidding at all, horowitz merely came in with a crazy high price and they agreed to it. If they had a bit of a back bone they could have done the deals for much less.
But it was quite hilarious to read how he convinced other thieves to buy his overpriced collections. I can imagine his sales pitch “you will be so respected if you become an antique books and manuscripts collector! You will be the cream of society. They will forget about your business dealings.”