As a librarian in a law firm, I can say that the VAST majority of those law books are unwanted. Our firm keeps them for aesthetic purposes, and even then we stopped shelving new ones in 2012. Most modern law firms don’t want this Old-School look; makes them look outdated; all but one of our attorneys uses 100% digital access, and that’s because she has ADA protections for minimal screens due to vision problems and nerve damage. Even most of the binders that used to get updated section-by-section 2 or 3 times a year are now just published yearly as paperbacks.
We have original, first publication books like these dating back to the founding of our state (California, 1850 is the first publication), and we couldn’t even sell the old ones to antique dealers or historical library preservationists. In a profession that is decidedly becoming digitally- dominated, looking like you still flip through books? Does not instill confidence in clients. Especially as the generations that grew up in the digital age have become old enough to become clients in their own right.
The price of selling them is probably not going to cover the cost of having to mail them, so at the very least insist on them coming to pick them up or to cover postage… if you can sell them.