Novice with vinyl & tapes needs help evaluating

I was recently able to cherry-pick a friend's vinyl & prerecorded reel tape collection prior to disposal. I found some interesting things that, I think, may be worth something. Jazz, vocalists, and big band music from Miles Davis, Stan Getz, Frank Sinatra, and others. Mostly mono with some stereo. I also took about ten stereo prerecorded 7" reel tapes (7.5 i.p.s.) in their original boxes that are either classical or big band from the mid-1950s. Also, a small set of boxed 45 rpm recordings of Strauss waltzes in mono from 1950. The last item is in perfect condition. The tapes have issues, including some mold and uneven windings on the reel. The LPs vary from good to poor in condition.

My intention is clean them up, record to CD-R anything I like, and sell them to dealers. There is a quarterly record show/sale near my home, and the dealers will buy desireable recordings from show goers. However, I am afraid that I might get ripped off, since I do not know which, if any, of these recordings are valuable. I have no way to listen to the reel tapes.

Is there a resource, aside from ebay, I can use to determine the value of this stuff, as well as qualify their condition in terms that a dealer would use?

If anyone would like more details on what I have, just post here, and I will post details as soon as I can.

Thanks in advance.