It’s a competitive market. Desirable games or good prices will attract lots of buyers. I think the best bet is to have cash in hand and be ready to buy immediately. A seller wants to get a good price with the meat amount of hassle so it’s to your advantage to be the easy buyer.
I wouldn’t hold a grudge against the seller. They either had a better deal or someone was willing to show up with cash sooner. Frustrating but it happens all the time.