correct reply to 1.b3 gambit by black

@Chessflyfisher There's nothing at all wrong with 1. b3, d5 for Black. It just leads to a different sort of game geography from the lines discussed thus far.

The thing about the lines with 1..., e5 and 2..., Nc6 and 3..., d5 is that Black is saying "I don't think you have enough pressure on my big centre and I'm going to challenge you in critical lines". As the discussion here shows, one National Master and some lesser mortals such as myself are struggling to find good play for White against a Black gambit in what has usually been thought of as White's main line with 4. Bb5. 1..., e5 is the critical challenge for the Nimzo-Larsen player to face.

With 1..., d5 Black won't get a big centre so easily. After 2. Bb2, Nc6 White can play 3. Nf3 or 3. f4 (rather like Bird's Opening) inhibiting ..., e5. Black still gets some perfectly decent positions playing the opening in different ways with different positions in mind (2..., c5 or 2..., Nf6 or 2..., Bg4 and so on; often playing more to control the light squares and less to challenge White's attempt to control e5) but these don't seem to be as critical a challenge to White's whole concept.

so here is the funny story, i havent played in an otb tournament since 2017, i played in the southwest class championship in the open section last week. and i did fairly ok (2 of 6) in a field with lots of IM and GM's but withdrew last 3 rounds since my sleep quality completely deteriorate., drew a NM even though i was winning most of them game , drew a 2100 last round (was already playing badly by then) and beat an IM with 1.b4 in round 1. 
two of my loses were with with 1.b3, the first was agaisnt a candidate master who played the gambit in this post. i bravely took the pawn and not remembering any concrete lines winged it. I fought valiantly with natural moves and my position quickly became -3, although i somehow got it down to like -0.9 in the endgame. Nevertheless i lost the good fight.
The next day i played a similarly rated opponent and to my great surprise i got the gambit AGAIN (turns out, they were roomates for the event XD), this time i declined the gambit after some prep the day before. I felt completely fine, during the trades, and calculated, f3, and qxd5 as variations, but completely missed the lethal g3! that occurred during the game. I feel i completely underestimated black's seemingly slow attack and felt i must have had advantage agaisnt such delicate black center. 
I feel like whites position is tricky after moves like h5 and f5 after white plays his improved french with ba3. Engine seems to think after h5, be2 and if bg4 take the pawn, then play c4 nc3 and castle queenside, black will recover the white h pawn eventually but white should be a little better. In my game, it actually suggests, 12. 0-0 !?! fearlessly castling into the storm. 
anyways thats the story behind the post. Never want to shrug after seeing 4.nge7 ever again lmao.

As a former 1.b4 player with some similarities in a few lines, would this not be a case where White should play the slightly counter-intuitive Bg3 instead of Bb2? That is after the trade on c6. Instead of 7.Bb2, you play 7.Bg3.

I play 1. …d5 followed by an early …Bg4 . White often will go into contortions to get that bishop out of there because they can’t push their d pawn to the center until it’s gone. If they play Nf3 take and double the pawns there and make them play a reverse caro tarkatower where it’s best to trade down to a winning endgame because that pawn structure is not great. Got the idea from a YouTube video can’t remember who it was.

i honestly hate playing against modern openings and i dont see them much especially this nimzo Larsen.

@trw0311 I mainly only play for giggles not grade these days, so I can afford to be eccentri: I'd be tempted to meet 2..., Bg4 with 3. h3 and 4. g4. Just for the fun of getting Black out of the book and moving towards tempi-up Grob country.

It's probably a rubbish line, but in practice off-balance opponents can do strange things.

This is a common response but black is slightly better. Jonathon schrantz has a YouTube video on this where he believes he discovered a novelty in this very position… black is better or winning in most variations. Check it out because there are a ton of variations. Bg4 if nothing else in short time controls can be a premove “check” because e3 is a very common next move for white. Aside from this silly “trap” pretty much every natural variation results in an equal or winning position for black. 
Nimzo Larsen players like to confuse their opponent by not following opening principles like with other modern openings so you have to play dirty lol

modern chess tends to more suspect of these trompowsky ideas than say, 40 years ago. Allowing bxf3 is not a big deal but a modern antidote is the following. after bf5 white can also play f4 and play it like a bird's opening.