Horror of horrors...
I've sold some tack on eBay, and I'm very careful to describe the item VERY accurately, welcome all questions, and always provide a return policy to make sure horse and rider are happy. I have had happy customers so far. Many other sellers do the same.
I have not purchased a saddle from eBay, however I have been helping a friend of mine, who's new to English saddles, try to find saddle for herself and daughter. I have never encountered so many clueless and rude sellers, and I've been doing eBay as long as eBay has been around. For the most part, when I ask about the condition of the saddle and ask for details like tree width, billet condition, flocking condition, etc, the sellers will try to be as helpful as possible. though in more cases than not, they have no idea how to measure a seat side, tree width, or even know what a billet is.
Do not trust that the saddle is as advertised when it comes to seat size, tree width or anything else. Ask very careful, specific questions and make sure the seller understands exactly what you're asking and how to measure.
Here are a couple of examples of how awful it can be:
-1- I asked for the correct seat measurement on a Stubben Rex, which was advertised as a 15" saddle. It was actually a 16". Seller had no idea how to find or measure the tree width. Then pulled it off the auction 4 days before end of auction, then sent me an e-mail asking how much I'd be willing to pay for it. I told her what I'd pay if she relisted it as a buy-it-now, and she told me that I should look for a saddle at Walmart.
-2- We found a saddle for my friend. The seller assured us that the panels were nice and soft and smooth. The listing specified a 7-day money back return policy, with no conditions. Saddle arrived with panels as hard as a rock. Seller refused to take the saddle back. Paypal had to settle the dispute, and the saddle eventually went back after a lot of headache and heartburn.
-3- We found a saddle advertised with good pictures but with very little concrete information. We asked about the tree width, seat size, flocking condition, billet condition, etc, and seller responded by telling us that we're too inexperienced to purchase a saddle and need to hire a professional to help us, then told us she'd report this incident to eBay if we asked any more questions. She called me an idiot for asking about the "flocking" - didn't I know it's called "stuffing"?
You can get some great saddles on eBay for a great price. There are some very honest, knowledgable sellers who will help you make sure you get what you need. Be sure you know exactly what you're buying, and be sure that there's a return policy. Pay only with Paypal so you have additional protection if you run into a flake.
And I do continue to look for saddles for my friend on eBay, because the selection and prices are great, and there are hardly any English saddles available locally on our side of the country. But I'm VERY careful. I've had much better luck buying saddles long-distance from Craigslist than on eBay.