I agree. Right now in order to buy a ship, you need to either press F, which isn't obvious or click on the button or press "3", "I" or "R" and then click on fleet at the bottom of the screen.
It isn't obvious that "F" hotkey passes you to the fleet screen to buy and sell ships in the planet screen. Could be better explained with: Trade goods or Hire crew(I), buy or sell ships (F), or refit(R).
For me the option reads "Trade goods or hire crew, buy or sell ships, or refit [I, F, R]" in 0.9.1a-RC8.
The fleet button is tiny and at the bottom. Normally that would be fine on the normal view, but it disappears on the planet screen and only reappears when you move to other screens.
On the fleet screen, the Open Market and Black Market are the most highlighted, taking away attention with "sell" and "buy" being rather muted and unnoticeable. "Buy" in particular is hard to read on the Black Market, being red on red. I suspect most people click on "Black market" and then cannot see "Buy".
And then there is Store button, with the buttons on the ship so generally similar to buy and sell, that it is possible to mix them up.
I think that instead of a fleet screen there needs to be a Fleet buy/sell screen, rather like the inventory screen, but for fleets.
Trade goods or hire crew, Buy and sell ships and Refit screen should be 3 different options on the planet screen.
I guess an argument can be made it will look like too many options, but it will aid clarity.
It's not a bad thing if there is more than one way to get to a screen.