I think I must apologize, as I have forgotten about the recommendation 1.e4 e5 2.Nf3 Nc6 3.Bc4 Nf6 4.d3 d5 5.exd5 Nxd5 6.o-o Bg4 7.Re1 Qd6. But I still think White is better after 8.h3 Bh5 9.Nbd2 o-o-o 10.Ne4 Qd7 Komljakov-Calderin, Olympiade 1998, 11.Bb5 with increasing pressure on e5.
As I have stated somewhere, Black's best chance for active play is 4...Bc5
A) 5.Nc3 d6 6.Bg5 (here Paddy and Markovich have the opportunity to teach about the dangers of castling early) Na5!? 7.Nd5 Nxc4 8.dxc4 Bxf2+ with interesting complications.
B) 5.c3 a6 (avoids d6 6.b4!?) 6.o-o d6 7.Bb3 o-o 8.Nbd2 Ba7 (and here one can teach about the meaning of transpositions) and the normal move 9.Re1?! Ng4! 10.Re2 Kh8 followed by f7-f5 leads to sharp play again.
Somewhere Markovich states simply 4.d3 Be7 or Bc5 with equal play. This might be formally speaking correct, but Black must play accurately to maintain that equality. That is what I mean, when I say that 4.d3 is the only way to play for an advantage; after other White 4th moves Black's play is easier. It is not by chance, that this system can be compared with the Closed Variation of the Ruy Lopez - another dangerous White system that is theoretically equal.
When I was still young, strong and beautiful I scored about 90% with 4.Nc3?! Nxe4 as Black.
So my opinion is: Black should prefer the Two Knights Defense to the Italian proper but prepare 4.d3 carefully.

On a beginners level I would recommend for White the direct continuation 4.d4 exd4 5.o-o Bc5 (Nxe4 is safest) 6.c3!? which also can be reached by 3.Bc4 Bc5 4.c3 Nf6 5.d4 exd4 6.o-o!? or even the transposition 1.e4 e5 2.d4 exd4 3.Nf3 Nc6 (Bc5 4.c3!?) 4.Bc4 Bc5 (Nf6 5.o-o) 5.c3 Nf6 6.o-o!?
I agree with Markovich that it is very useful to get experience in these lines - as soon as one gets stronger, it is handy to know how to meet all those Italian/Scotch lines with confidence. My experience lead to the following game:

Mungroo,F - MNb [C55]
Interclub Suriname, 2002
1.e4 e5 2.Pf3 Pc6 3.d4 exd4 4.Lc4 Pf6 5.e5 d5 6.Lb5 Pe4 7.Pxd4 Lc5 8.0-0 0-0 9.Lxc6 bxc6 10.f3 f6 11.exf6 Dxf6 12.c3 La6 13.Te1 Dh4 14.fxe4 Df2+ 15.Kh1 Lf1 0-1
In case you think White is an absolute nitwit, he drew with GM Campora on the last Olympiade.

Quote:


In 6...Bg4 line, after 7.Re1 Qd6 , Black's position seems to be defendable, or am I missing something? 

Ah yes, just sussed it! The Radev--Inkiov score as given on BigBase seems to make sense if you replace 16 Re2?? with 16 Re4!

I find the variation:1 e4 e5 2 Nf3 Nc6 3 Bc4 Nf6 4 d3 d5 
5 exd5 Nxd5 6 O-O Be7 7 Re1 O-O 8 Nxe5 Nxe5 
9 Rxe5 c6 10 Re1 Bd6 11 Nd2 Qh4 , very similar to Marshall gambit

"Officially" this line belongs to the Bishop´s Opening 1.e4 e5 2.Bc4 Nf6 3.d3 (ECO C24), there you´ll find plenty of material to 3...d5?! 4.exd5 Nxd5 5.Nf3 Nc6.
Curiously 2.Bc4 is the only white setup in the Open Games where the immediate counterstrike d7-d5 seems to be simply bad. 
White continues with 6.0-0 and now Black has serious problems to develop as White will pressure on Pe5. It´s impossible to give a forced line to white advantage but if you simply play some moves further and analyze you´ll see. 6...Nb6 runs into 7.Bb3 Bd6 8.Ng5 0-0 9.Qh5 +- and on something like f7-f6 White will open the game with d3-d4 and advantage. After 6...Bc5 7.Re1 0-0 White has to be careful (8.Nxe5 Nxe5 9.Rxe5 Bxf2!) but he can play 8.Bg5 or 8.c3 with d4 to follow. For 6...Bg4 conceeding the bishop pair look at Larsen-Berger, Amsterdam1964.
In all these lines White should be += or better!

1.e4 e5 2.Nf3 Nf6 3.Bc4 Nf6 4.d3 d5

what do you think about 4...d5?

can this move be refuted?