Are these results normal? (Yellow letter campaign)

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So, I started a yellow letter campaign and have sent out about 100 handwritten letters to non-owner occupied properties. I got ONE call from a man and his wife that owned 2 lots of land (right next to each other) in a very hot area in Atlanta. They wanted nothing less than $500k for both lots (combined). We did the research and saw that it wasn't a bad deal and made an appointment to meet with them. 

We drove to see the land the day before the meeting and saw "For sale by owner" signs tacked onto a tree. The houses surrounding the land were selling for about $800k-$1.2 million. We did our numbers and figured we would try and make them an offer. 

So the next day we meet with the husband....he seemed friendly but not really motivated or receptive to our offers/interest. AND on top of that a real estate agent had come through, removed their signs, and replaced them with her own signs. He told us they were going under contract with the agent in 2 days and to talk with her if we were interested. (So frustrating! lol) So we followed up with husband again the next day on the phone and he was a little grumpy and said that if he were to take our offer he wants nothing less than $500k and we shouldn't need more than a day to close/get the money (we planned on wholesaling the land to a developer). At this point we decided to let it go and just follow up again in a month or so.

So long story short this was discouraging. I plan on writing more letters soon (I have a list of about 800 people) but I feel like maybe the sellers won't be motivated in this type of market (Atlanta is a huge seller's market at the moment). I wrote up bandit signs last night and will be putting them out. I also plan on driving for dollars all day tomorrow.  Annnddd... I'm in the middle of completing my exams to become a licensed agent. So there's a lot going on and I feel a little scattered. Does anyone have any advice or even words of enlightenment to get through this little rough patch lol? Does it sound like we potentially missed out on a good deal?