Maybe I just got stupid lucky. I bought my dressage saddle, a 35 year old Passier with a medium wide gullet and 17 inch seat, and it fits just about every horse I bother putting it on (even though every one tells me Passier runs very narrow). It fits me too, and I am superbly happy with how it fits my legs (flap is long enough for my leg). All I pad with is a thin line and a western saddle blanket or dressage pad. I ride some fat Walkers and QH's lol. Stupid lucky that I have had no fitting problems yet. And I got it off ebay with a piss poor description of its "aesthetic imperfections" meaning the broken stirrup bar wasn't named, but the tree is still good and the leather in great shape despite the smell of cheap lotion sticking to it. I had to deal with outrageous shipping charges too. Plus the seller waited until the last darn minute to ship it to me. Very aggrivating.
So you have to give and take and hope you get lucky. I passed up a 300.00 Stubben close contact dressage for a slightly cheaper Passier, and I'm happy I did.
Think of it not as a failure but as a success in how not to do it.
Don't look in a horses mouth for a gift.