It's pathetic if you're ordering from reputable sites such as Amazon (particularly if you stick to Amazon itself, rather than Amazon Marketplace). 3 missing items out of 5000 might be a realistic figure when ordering from such websites (with some of those being the fault of the Post Office, rather than the sellers).
If you're ordering from eBay, it's still very poor. Probably fewer than 1% of Ebay purchases fail to arrive.
However if you've been ordering from sources in China, or from obscure websites which you've not checked up on beforehand, it might be quite a good success ratio!
Chris