There are many Buffy the Vampire Slayer and Angel props for sale on eBay all the time. The trick is knowing what's real and what's fake.
Throughout my dealings on eBay for Buffy props I've only found one seller that actually sold authentic Buffy and Angel props and that was VIPfanclubs. They sell props directly from the Fox Archives and give out an authentic COA (Certificate of Authenticity).
All the sellers say that their props are 100% real because they want to make the big bucks. Sure I bet there are some real Buffy and Angel props on eBay that don't have real Fox COA's, but it's too hard picking through them to find it out for sure or not (plus it's not worth spending huge amounts of money for something you think is real, but you find out later it's just a good copy, all that money would be wasted). You just have to watch out for big scams that promise something very iconic. Something key to an episode or a season should have been sold by Fox, it should have an authentic Fox COA. An example, if you saw an eBay seller selling Buffy's Hunga Munga weapon from "Anne" in season 3 without a Fox COA, you should be very suspicious since something like that would have been sold directly from Fox since it's such a key prop to the show.
So just watch what you buy, if it looks too good to be true, it usually is (unless it has a Fox COA).
If you have any questions about anything feel free to send me an email.