What is the refutation to 1.d4 Nf6 2.Bf4 c6 3.e3 g5?

Why not just Bg3?

@blueemu I would link their repertoire they've compiled but chess.com doesn't want competitors' websites mentioned.

After Bg3 they say they play Qb6.

@FishEyeedFools Yes that is the main idea. So what should white do instead?

Just play 4.Bg3

I don't play the London, but doesn't the knight go to f3 in any case?

So just play 3.Nf3

But also you shouldn't be afraid of 3.e3 g5. It will turn into a normal game where the inclusion of g5 is not ideal.

@FishEyedFools (Sorry I didn't read your entire diagram)

Okay this is their book after Bg3

@godsofhell1235 After 3.Nf3 

What here?

@FishEyedFools sorry I took longer on my last comment

@FishEyedFools Wow, that line looks pretty good. I'll see what they think about it

@FishEyedFools He says he'll play 7...d5 after 7.Ne5. What now? (Really sorry if I'm bothering you)

Ok so here is the current line: 

After Qc3 does white still have compensation? (Thanks so much for your help on this- it's really nice of you and again let me know if I'm commenting too much)

I don't like b3, but ok, so you showed me what happens after 3.Nf3.

Now let me see what happens after 3.c3. This seems to shut down black's ability to force a non-London-ish position.

I give 3 variations on move 3 for black (g5, Qb6, and h6)

To be quite honest, this line actually has much more merit than many of the other posters give it credit for. There's a lot of connections with ...g5 in the Trompowsky and Scotch (see the Kasparov-Anand match). It is certainly viable as a shocker weapon against London practitioners, but that doesn't mean there isn't a good antidote. Of course, the simplest way out of this is just to play 3. Nf3 and avoid the whole thing, but I'll see what I can pick out of it:

So it appears that 3...g5 is not so easily "refuted" after all...

@godsofhell1235 That seems good! Maybe we're getting somewhere. After Qc2 he says he'll play d5, but I think that just transposes back into normal London Lines. (in that case maybe Qb3 should be played instead of Qc2)

And then he says after d5, he's still super persistent and he wants to play h6 and g5 and castling queenside. So you're super sure that this is a demerit for black rather than a benefit? Again, these guys are super attacking players who consider 1.d4 a blunder

The new line they just discovered 

There are no major problems for white here, are there?