Most of the time old sets of encyclopedias are worth nothing. If the sets are very old there might be some artistic quality in the old pictures that are in them. For instance pictures of cities in the 1800's or even more recently. These pictures could be cut out, enlarged and put in frames. Especially pictures of places that have changed or no longer exist. I am not sure about copyrights pertaining to them but if they are for your own use or for children's projects and not for selling it probably would be fine.
By Lilac from Springfield, MA
ThriftyFun is one of the longest running frugal living communities on the Internet. These are archives of older discussions.
I have a 30 year old set of Encyclopedia Britannica in almost pristine condition. I must downsize and dispose of them. I have called thrift shops, rescue mission, library and no one wants them.