As someone quite new to punting, I'm definitely finding, at least so far, it's not nearly as simple as I had hoped it would be. I only punt when traveling to London for business, and I'm usually there for just 3 or 4 days at a time.
I guess naively I was attracted to punting because I thought it was going to be a way to have sex with nice looking women with no strings, and with a guarantee of getting at least close to what I expected from the transaction.
So far my limited experience has been similar to the OP. Since I don't live in London and only have a few days at a time for this hobby, maybe once every month or two, I too find it difficult to actually arrange and complete bookings that work with my limited availability. I really don't have the time for plan B's and C's, so when plan A's don't work, that it's for me for that visit.
Even though I now choose wg's carefully with the help of the UKP recommendations, too often I don't hear back from the wg, or they're not available when I am, etc.
I'd like ideally to find a few regulars who are reliable and know that I am too, then stick with them, but I suppose that will take some time.
All in all, at this early stage for me it does seem like more work and uncertainty than I was expecting...