Here's my take on it from the seller's point of view.
#1, I don't ever try to push someone into buying my horse. There's not any of that, "OH but I want YOU to have her.". So to me, that's a stupid move on the seller's part and made you feel obligated.
#2, No horse is SOLD or off the sales sheet without a signed contract AND a 25% NON-REFUNDABLE deposit to hold the horse until the agreed upon date when the balance is paid.
#3, No sales deal is truly finalized until the cash is in my hand and the horse is on the trailer headed down the driveway away from here.
#4, I figure that 99% of the people I deal with are "Hoof Kickers" and won't follow through with buying the horse, no matter what they say.
So, for courtesy, check out the gelding and make your decision final quickly and release the mare ASAP if you're going to. If the mare really has several buyers ready to jump, then you don't want the seller to lose out because they TOO found other horses.
As a seller, I wouldn't even be mad if you backed out at this point as long as there's no signed contract and no deposit has been paid. If you backed out after signing the contract and giving me 25% down, I'd still shrug my shoulders and figure I'd rented the horse out for $625 for a few days, not a big deal.