It depends on what you buy and where you live. If you buy relatively small amounts of any tired old blob (common, non-denom bullion bar) and you have easy enough access to a bullion dealer who doesn't charge taxes on whatever blobs he may happen to have on the shelf that day, then you may be better off buying from the dealer. But many sellers on eBay ship free and charge no tax. I've never had problems on eBay and I have often gotten much better prices than from brick and mortar dealers.
If you are looking for semi-numi coins, in most cases eBay is a much better source than a local dealer who may take weeks or months to get what you are looking for.
As for fakes, the buyer protection for buyers is about the best there is on the web. But if you buy from reputable sellers, you needn't really worry.
I recently bought a few graded silver Canadian maple Leafs on eBay through APMEX....the same coins APMEX was selling on their own official site were listed at more than twice the cost on ebay. APMEX obviously goofed on the eBay listing and I took advantage of that.
Another eBay seller just yesterday told me of the same exact thing that happened on eBay with APMEX (different graded coin) but he made a winfall because he was able to buy more than 20 graded ASE's at about $34 and is easily selling them for $60-$64 on eBay (PCGS price guide value is close to $100 for these coins if I remember correctly).
The point is, I find that eBay is a great place to shop and I have never knowingly received a fake. I am selective as to who I buy from and if the price is way too good to be true...I find out more about what is being offered for sale before I make the purchase.
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