Why is it considered a disadvantage to accept Queen's Gambit? How should I play to take advantage of an accepted Queen's Gambit?
(All online guides I've seen simply state not to do it, but don't explain why it's bad or how to take advantage of it.)
White has a slight advantage in the Accepted line, but it will depend what level you play at. Even at the higher levels both Anand and Kasparov have played it.
You give up the center in the QGA as black, but white has an isolated Queen's pawn to deal with. There are too many alternatives for the QGA to go over them all here.
In general, white is taking the center, and hopes that his advantage will compensate for the pawn. A very logical move then is 3. e4, grabbing the center with a pawn duo, though 3. Nf3 has been more popular.
If Black tries to hard to keep the pawn, he'll only hurt himself.
The reason it's discouraged for lower-rated players is that black gives up a center pawn and allows white to develop his bishop with a gain of tempo - two things we are trying to teach the players not to do.
However, in higher levels it's considered ok, since the half-open d-file gives black control of d5, and in many lines white's d-pawn becomes isolated.
Of course, in the end, at lower-level play the opening doesn't really matter.
I'm not sure it is a disadvantage. Here's a quote on the QGA entry on Wikipedia:
At the end of the 1990s, a number of players among the world elite included the Queen's Gambit Accepted in their repertoires, and the line is presently considered sound.
It has gone in and out of favor over time, but apparently it's in vogue now. Maybe it's discouraged for beginning players?
Generally, the Queen's gambit it's not considered a true gambit, because white comes out ahead with an accepted queen's gambit. White is offering a wing pawn in exchange for a center pawn.
Theoretical disadvantage of an accepted Queen's Gambit:
Now white has a commanding control of the center of the field, and is not down any pieces. (though the queen is out and exposed very early)
At least that's how it was explained to me 20+ years ago.
Not that this is the way it's usually played, but white players consider that other things they can do with an accepted queen's gambit are better than this.
Accepting the queen's gambit pawn is considered disadvantageous under the old, German school of thought. In fact, Tarrasch would play, 1. d4 d5 2. c4 e6 3. Nf3 c5 as BLACK, offering a QB pawn to white.
The newer, "Russian" school of thought is that captures c4 is a fighting move that puts a thorn in White's side. Sometimes the pawn can be held if White emphasizes the king side (e.g.) 3: e4 e5; at other times, recapturing the pawn takes White out of his way and dulls the attack.