Really a tough issue. My guess is that if it is full of really rare records that are in mint or near mint condition, a really knowledgeable dealer could come in an cherry pick the collection and get 95% of the value of the collection in about 50 of the records. Remember the scene in the movie High Fidelity where John Cusack's character visits this woman who is offering her husband's collection of records (while he is away cheating on her).
For example, (I know classical not jazz) if the collection has the 3 Johanna Martzy Bach Sonatas and Partitas on original EMI pressings and 3 of the Leonid Kogan Beethoven, Brahms and Tchaikovsky Violin Concertos on EMI SAX Blue/Silver label Stereo (all in near mint) those 6 records would be worth about $1500 to $3000 each. There are jazz records that may have similar values.
On the other hand, lots of great old classical records (including many of the RCA Living Stereo, Mercury Living Presence, EMI ASD, Decca SXL etc) are worth $10 to $40 each in excellent or NM condition, while others can be worth several hundred each.
They really need a list of the records with the exact label (and even sometimes the exact stamper information - like RCA LSC-2436 1S Pines of Rome) and all important condition - best play graded at the top end. Then a fair evaluation can be made.
Larry
PS. It is really, really important that the seller does not allow anyone to come in and pick out a few of the records. Many times I've seen collections and I can tell in maybe 10 minutes or less whether someone has cherry picked it. If your friend doesn't care about value or rarity, then maybe buying such a collection makes sense, since almost all of the value of the collection will be gone and the remaining records would be worth maybe $2000 to $5000 in a package deal.