[78-L] Vintage Sheet Music Question

[kil at roadrunner.com.invalid]

A friend has taken on the task of going through someone else’s  collection of approximately 700-800 pieces of piano sheet music for the purposes of disposing of it.  He’s trying to save it from the landfill.
The only thing I know about the collection is that it is in very good condition and some go back to the 1900's (publishing date).  And I believe it was collected in the Dallas area if that means anything.
Does anyone have insight as to what to look for while going through this collection, one by one?
And any ideas where best to sell it in its entirety?
He has no Ebay expertise, nor do I.
Are there any reputable private dealers who might be interested?
Any leads appreciated.
RayK