We've just gone through something very similar. We ended up selling to horrible buyers, and experienced almost as severe a level of insult as you have. In the end, we lost $300,000 on our home, but feel good to have gotten out from under the expense, and will most likely be relocating to a new state for a new job anyway. They were "cash buyers," so our agents tolerated everything they were put through.
Our buyers took forever to make up their mind as well, although they were "infatuated with the cleanliness" of our home, according to their agent. They also wanted pre-approval from the HOA to install a fence, trees, etc. Since my DH is President of our HOA, he tried to assure them that if they wanted to put something similar to existing fences and landscaping, it should be approved. The buyers kept insisting that they needed pre-approval. Finally, hubby forwarded them a letter from the HOA Management Company stating that they could only approve it once they had architectural plans etc. We told their agent that we were unwilling to incur the expense involved in hiring an architect to draw up official plans on their behalf! We reminded them that if they wanted to put in something similar to what's already been allowed in the neighborhood, they couldn't be turned down by the HOA. If your buyers want to put in some kind of aquatic monstrosity, then they should expect to have their request denied! Our buyers finally got it, and we moved on to their other contingencies.
They wanted the house inspected, and appraised. We came out well on those, (actually appraising for more than the agreed upon selling price, although we weren't allowed to see the figure arrived at!)
Then, the buyers made some poor schmuck get up on our snowy roof to verify that the roof was OK. This is a four year old house, by the way! The A/C couldn't be tested, since it was colder than 65 degrees outside, and apparently, you can actually damage the unit by turning it on in that situation. So, the buyers made the two real estate agents put into the contract that they'd pay to fix the A/C, should it not operate correctly in the Spring.
They also tried to move up the close date, which was impossible, since by the time the contingencies were lifted, we had two weeks to pack ourselves, get an apartment for our son, find a home for our chinchilla, sell our exercise equipment on Craig's List, etc. A complete nightmare, but we got it done.
So, now we're staying with our good friends down the street, and three weeks later, they still haven't moved in, and have left the house pitch black at night, and have even turned off the landscape lights!
We ended up leaving the leftover paint in the basement for them, simply because we were too worn out to take it with us! So, I definitely feel your pain! The buyers' agent told us, "Well, you can be just as awful to the sellers when you buy your next home!" DH said, "See, we'd never do that to someone." So, I figure the karma will come back around eventually.
Hang in there and hope that your buyers gets their acts together and stop pushing for what doesn't exist. I think if our buyers had dared to ask for our financials, DH would have walked away right then and there. We were just lucky that it didn't occur to them!