I have bought several saddles online, and some, I have resold, since they were purchased on eBay
and not returnable. However, I have basically broken even, and did get exactly what I want in my budget that way. When you look, like has been said-know what fits you, and your horse, as well as what you like and what fits what you do (roping, reining, etc). It is critical, if you are looking at something like eBay, tacktrader, etc, that you know not only what the seat, gullet, etc measures, but please look at HOW and WHERE they measure. Many people measure in all different places, and that is the only way you can compare it to what you actually need and what will fit. For example, someone may say a saddle it a 16, when in fact it is 16 to the cantle stitching, but padded to a 15.5.....which won;t work if you need a 16.
Another way is, yes to go with one from a place that allows returns-but shipping can get really expensive.
Good luck! Happy shopping!