Is this the norm?

I've been trading on Audiogon for 2 years and have had great experiences as both a buyer and a seller. Then I posted an ad for a learning remote control. I received two email within 20 minutes both buyers commiting to buy the unit on the spot. I emailed the first respondent and said the unit was his. I heard nothing back so a few days later I emailed him again. Nothing. After a week and a half I emailed him again expressing confusion because he had seemed to really want the item. I finally heard back from him saying he thought it was a different model, the model # was clearly in the title of my ad, and he didn't want it. Fair enough. I contacted the second potential buyer, explained the deal had fallen through, and offered the item. The buyer quickly said yes, I agreed to pay shipping and he said he'd have payment in the mail by Monday. I waited until the following Monday and emailed him inquiring about the payment. He responded by saying he had forgotten all about it, thanked me for reminding him, and said because of all of the other transactions he had conducted over the past week he couldn't buy the item now. This is the frist time something like this has happened to me once, let alone twice for the same item. So I must ask, is this normal and have all of my other pleasant, professional transactions been abberations?