You say you agreed on price and a location for in-person exchange. My guess is someone offered him the amount he was looking for AND offered to come pick up the game rather than him having to meet somewhere.

I don't know the details and timing of your PMs, but as someone who just sold a game, I know that a seller often gets multiple offers of differing amounts, people wanting to meet halfway, have the game delivered/shipped, etc. Also, buyers can be vague (e.g. "I'm interested") or want you to hold the game. At the end of the day, the seller is going to go with the deal that is some combination of the best cash offer and fastest/smoothest transaction.

In your case the seller backed out, but the reality is a lot of buyers back out, so sometimes the seller will go with the quick sale rather than some scheduled meet-up.

Better communication could definitely help a lot of these situations.

I just want to clarify. There's a difference between a seller selling out from under you while you're en route and a seller not willing to hold a game for a buyer when other buyers are lined up. That doesn't sound like what's being described here though.