eBay is completely inconsistent (I know that should be pretty obvious, since there is multiple people involved rather than a single company). I've seen some books sell for INSANELY awful prices, however I have an autograph copy of Mark Wilson's Course in magic for $0.99, And an autographed copy of The magic of Micheal Ammar (I brag about that every time I have the chance) for $25. When I did the wand street Journal, I had to sift through A LOT of complete and utter garbage prices, to find a decent one, and I kept the good ones to my self (Sorry about that...). Not going to lie Looking back I bought a copy of Tarbell's course vol 1, for what was honestly a pretty bad price.
To conclude eBay can be a great place, but also possibly the worst so I would suggest it as long as you know the actual retail price.