How not to play the chess opening.

Occasionally I catch somebody in an old trap.
I had a new victim recently.
The trap is starting out as a normal Queens Gambit.
That is 1.d4 d5 2.c4
this is an excellent opening, the next move black made is also a normal move, but it might require
more to play this.
2...dxc4

The reason I say this might require more, is the fact that black has relinquished his queens pawn for a bishop pawn.
Besides that it is a decent enough opening.
However here I play an old move that contains a little bit of a trap.
3.e3 This move attacks the pawn on c4, but a more hidden thing is the possible Qf3 attacking both the diagonal towards the rook on a8, and the vulnerable point on f7.
However one of the bad moves against e3 is when black plays b7-b5.
Which happened in this game, and that is the trap.

After 4.Qf3 white should be much better.
The variation 4...c6 5.a4 a6 6.Nc3 Bb7 7.axb5 axb5 8.Rxa8 Bxa8 9.Nxb5 does not really work..