It happens all the time. I call on an ad 12 minutes after it's posted. The guy says, "I have had 6 calls already, maybe I underpriced it". Usually he says he is going to raise the price or take offers. That's when I bail out unless I REALLy want it and make a slightly higher offer.
Although a week ago a guy says he had a bunch of calls on voice mail and I happened to get him answering. He said just come and get it so it's over and out of my hair.
You will find a bike that works for you and at a good price if you are persistent and patient. You will be told by many that you need to go and buy the bike and not ask first if it's a good deal. It will be gone already. Good luck.