Altho it may seem you had a legitimate right to offer $20 on the bow, in practice it engenders ill will, and in my experience, the seller almost always sells it to the first guy, sometimes even for the lower price, on the principle that the other guy was there first. I went thru the same thing as you have. It's best to let them negotiate the deal, and hope it falls through.
You said your nemesis was "a strict jewelry buy", yet your story begins with the guy buying a recurve bow. So he's not strictly a jewelry buyer, and this makes me think you are bending the story a little bit. I'm not saying the guy who dinged you didn't relish the opportunity to ding you, but I very much doubt he spent money on something he didn't really want just to ding you. He's probably unemployed, and since he's in his 60s nobody wants to give the guy a decent job. He's too young for SS and medicare, but old enough that body parts are wearing out, and he's probably trying to keep his head above water. I say give him a break. Those DS games are reliable, safe sales, he'll make several times what they cost, and that guy knew it and needed it. He may have rubbed it in just slightly, but hey, he remembered you had meddled, and he was just letting you know that he remembered.
I have a 17 year old and he used to come with me to sales when he was your kids age, so what I'm about to say comes from my experience as my boy's primary caregiver since he was an infant. I'd say this was a teaching moment, and let him know that you were just a little late closing the deal; the owner did not know you weren't just looking. Don't be ranting on the other guy, that's not what you want your kid to learn. He should see that you take responsibility, and that you don't blame others when in fact you had the opportunity to have purchased the games for him, but didn't do what you needed to have done in those circumstances.\
Having said all that, I'd probably have made a few choice comments to vent steam, then explained to my son that I was just venting, and that losing the carts to the other guy was my responsibility, not the other guy's, not the seller's, and certainly not his.