i would say yes its safe to buy speakers off of ebay.
just google the brand name and model if you are not familiar with them, also pay very close attention to the sellers feedback. if they dont have much or are not close to 100% positive.. then you might browes through their feed back ratings and read why they are not getting positve from their buyers.
if they have good feedback and they have decent pics and good descriptions then go for it. also look at
www.audiogon.com this site specializes in higher end audio equipment.