I haven't done it no, but I'm sure it's worth a try. My guess is that you should only buy well known brands of saddle, or brands that are liked and loved because non-branded ones are ten a penny on eBay and don't seem to go for much.
Maybe if you're prepared for making money the slow way you could try it in reverse. Buy cheap saddles off eBay and sell via tack shops.
The last saddle I had fitted, the saddle fitter said he'd got a customer who bought branded saddles of eBay dirt cheap, where the seller had provided poor photos or description and therefore bidding had been low.... and had then taken them to him to sell on. He reckoned on average she made £100 per saddle even after his 20% fee had been taken off!
Not a bad result!
On the other hand, whenever I've tried to sell saddles through Tack Shops they've sat there for 6 months and never sold!
Remember that if you are buying stuff with the intention of selling it on, Ebay will class you as a business seller and you will be liable to pay tax to HMRC on any income.
I think its quite hard to do. Ebay fees are very high and currently even nice saddles with good pics are not fetching alot. I've sold a few old saddles of mine which I bought for a horse and they didn't fit. After the fees it was hard to make anything much and it took a long time for them to sell. I think if your prepared to have the money in the saddles for a period of time it might be worth doing. Also with Ebay if your a business you have to accept 'returns' and they are very much in favour of buyers so you will loose the postage cost if someone decides to return the saddle to you so IMO better selling through other sites..