When they play d4 d5 f3? (is that a book move?), Nc6 e4 trying for a break in the center (of course you might not play Nc6 but it could be an option for you now), you can safely play dxe4:

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f3 is used in a variety of QP games and it could be your opponent is trying to steer/sidestep to a personal setup.  It seems many 1. d4 players specialize in facing Nf6 or d5 but not both and so an attempt to avoid learning.  If White is playing this he needs to look at BDG ines for progress.   The lines you give for white are too conservative.  

Thanks but which lines? I could understand it if you were saying the opening ones, but most of the moves ive checked and are correct.
Edit: I see now, you mean things like some of the opening moves (eg e4 and Bb5), and also like mini-blunders such as "Nxd4?". Those are lines i gave that white might possibly play or is tempted too. The best line i have not included in there for some reason... and i don't plan to either o.O

I think he meant that if White wants to play 2.f3, he'd probably do best to play it in Blackmar-Diemer gambit style -- sacrificing a pawn by letting Black take on f3, for quick development.

The Blackmar-Diemer gambit is 1.d4 d5 2.e4 dxe4 3.Nc3 Nf6 4.f3.

In your move order, it'd probably mean a move like (1.d4 d5 2.f3 Nc6 3.e4 dxe4) 4.Be3!? aiming for 4...exf3 5.Nxf3, with a sort of Blackmar-Diemer where Black's knight on c6 looks a little odd.

Oh right yes, another line instead of the "d5" one i gave. I'm learning here =D.