Thanks to everyone for all the info and encouragement! I re-read Lonnie's book and I realized that I probably got discouraged to quickly and I dropped the ball too early. So, I called the guy back (as suggested by Lonnie) and ask "If I could pay you cash today, what is the best price you could offer?". (I already asked that the first time we met....but, apparently, asking multiple times is okay). So, I did that, and he dropped the price to $3,000 (from $3,750). I told him I would think about it and he asked me what I would pay. I told him I'd have to ask my husband and get back with him (Lonnie suggests not making an offer at that point.) Then, my husband and I went out of town for the weekend and I called him as soon as I got back on Sunday to set up an appointment to look over the home again and he had already sold it. So, my next step is going to be to call the park manager and ask if the buyers were approved.
So, I've learned that just because a seller says that is the final price and it is FIRM, doesn't mean they won't change their price tomorrow or next week. And, just because they have a buyer, doesn't mean the buyer was approved by the park. So, I'm going to follow up on every deal and I'm sure sooner or later I'll get a deal done. :)