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e f g 1 h Why it works
Black is a pawn up and wants to keep it: 3...b5 props up c4, and after 4.a4 c6 the pawn wall looks solid. But 5.axb5 cxb5?? — the natural recapture 96% of players make at 1400 — opens the a8-h1 diagonal while the rook still sits on a8. 6.Qf3! hits the rook and the b5 pawn at the same time, and nothing holds both: 6...Nc6 7.Qxc6+ comes with check (nothing defends the knight — the d-pawn left on move one), and after 7...Bd7 the queen simply steps back with 8.Qf3, a piece up for a pawn. The greedy 8.Qxb5?? would hand it all back to 8...Bxb5. The other answers are no better: 6...Bb7 7.Qxb7 (the rook on a8 does not defend b7), 6...Qc7 7.Qxa8, 6...Qa5+ 7.Rxa5 — the a-file opened along with the diagonal. Alessandro Salvio published the idea in 1604.
Refutation
Give the gambit pawn back: 5...Bb7 or 5...Nf6 instead of recapturing — +1.3 for White instead of +3.2, and the rook is off the diagonal. After 5...cxb5 there is nothing left to save: every answer to 6.Qf3 costs material. Better still, do not build the wall — after 4.a4 play 4...b4 or 4...a6 rather than 4...c6.