What to do/

Sell piece by piece on eBay or Discogs or something like that, which is a great deal of work for a nice-sized collection, or sell in bulk to a store or person, and they'd receive nowhere near as much, but is much more easily done.... I don't know what you'd consider 'getting taken', but likely won't get anywhere near as much as they'd like to think. I wish him luck. 

Bad part of a D.J.'s collection is the abuse that most of records have probably suffered. All the handling and back cueing (depending on what he played) may have hurt them.

Make a Discogs account. Add all the records with their condition. Put whole collection for sale.

Sell the whole collection to 1 buyer. You’ll be lucky to get 1$ each. Let the buyer sort them out. Most records aren’t worth much more than that wholesale.