I'm buying a saddle online at the moment, waiting on it to be posted (US to Australia). I've also sold a saddle on Ebay
, and have had friends buy online.
There are risks involved with buying one online but I think that, being smart you can make it work.
First - don't buy unknown saddles. Buy a brand you have tried on your horse or sat in before. If you're looking at this Circle Y, have you sat in a similar version? Have you tried something similar on your horse?
Does the ad have a lot of information, have you asked the seller various questions? Are their lots of pictures? Do they have a good rating? If they do seem pretty legitimate, then buy one through PayPal, if it's been misrepresented you do have some sort of recourse.
Another thing is buy it at a good price, so if it doesn't fit, then you can resell it. My friend bought a barrel saddle from the US, rode in it for six months then sold it, losing maybe $100 or so, because he paid a reasonable price for it in the first place.