I didn't buy my headset on eBay (it hadn't been invented then), but buying there is safe if you follow the common sense rules:
- Don't buy off anyone with fewer than 10 feedback (absolute minimum) unless the value is insignificant;
- Don't buy off anyone with lower than 98% positive feedback (most folks don't leave negative feedback because they expect to receive the same by return), and look to see if there are any "hidden gripes" in feedback, or "mutually withdrawn" feedback and what they said;
- Pay with a credit card (via PayPal if the person has the £500 guarantee);
- Never, ever buy "outside" eBay if someone makes you an offer to do so;
- Check that the "Buy it Now" price is sensible (I've seen some that are over the UK shop retail price);
- Decide before you start what your maximum bid will be, and don't go over it.
I've bought over 250 items on eBay over the years, only had a couple of "duds" (they were promptly refunded), and one attempted scam which eBay spotted and stopped before I did.
I'm very happy with the eBay experience, but I've heard others speak very differently. I suspect they didn't follow the "rules".