user7218: Among chess players circulate the idea that any gambit should be accepted. It's an old and popular idea; if you don't want trouble, accept the gambit. Should this be consider a valid principle?

user4362: I think the way you put it this is pretty much just wrong.
There are a lot of pawn sacrifices in the opening that should not be accepted, something that is obscured by the fact that sacrifices that shouldn't be accepted are often not even called gambits (Though they still are gambits of course.)! The logic is along the lines "I play this move and now my opponent could win a pawn, but I know that he knows that that's no good, so I didn't actually sacrifice anything.". 
Mostly sacrifices that are regularly accepted in tournament play are called gambits in the official nomenclature, but even among those, the best way to counter them is often to not take the pawn, or to return it as quickly as possible. 
Certainly taking the pawn isn't usually the way to "avoid trouble".
The saying as I know it rather goes: "The best way to refute a gambit is to take the pawn." And I would interpret as meaning that if there is a refutation it is likely to be in the variations where you take the pawn. It does not mean whenever you take the pawn, there is going to be a refutation.

user446: I am not sure who may be these chessplayers who think gambits should be accepted. Certainly not the many (including most world top players) who do not reply with 2. ..., dc4 after 1. d4, d5 2. c4. 

user8160: In addition to Glorfindel really good answer (+1) I would like to add that you can also use gambits to fill position with traps. The person who is not familiar with the gambit may get lost in the suddenly created 'minefield' position where a 'single step' from the right line of moves leads to a disaster. 
It's also important to note that in many of the gambits you need to know how to decline it properly as well! 
Also there are some gambits that you SHOULD accept (to get a better position). For example Latvian, where after 1. e5 e5 2. Nf3 f5 the main line is 3. Ne5!? Even though you may know that it's the main line for white you really gotta be careful with your subsequent moves, because the position gets incredibly sharp, complicated. 

user9030: Gambit's are sacrifices which are played hoping to get development advantage and/or initiative in opening.
So if you accept the gambit, and if the opponent can't consolidate development advantage and/or initiative, you will end up better. But if you decline, opponent will get advantage generally (This is where that principle comes from). Gambits are generally advantageous for sacrificer when they are declined.
However, some gambits really loses advantage when declined. For example:
[FEN ""]
[Title "Smith-Morra Declined"]

1. e4 c5 2. d4 cxd4 3. c3 (3...dxc3 4.Nxc3 {White has development advantage, and is happy }) d3 4. Bxd3 { c3 is not available for White Knight, if
White plays c4, then whats that Bishop on d3 doing?}  ( 4. Qxd3 { White Bishop
is blocked and c3 is not available for White Knight.})  

Black simply expels White's fast development plan by declining the gambit. Now, White has opening problems to solve, not Black. 
I play myself Smith-Morra with Whites, and hate it when declined. It's much more harder to play in declined variation.
So that principle is not valid. You should really think about the outcomes of accepting and declining before deciding.

user7297: This is really dependent on

which gambit
the style of play you prefer.

For 1, consider the King's Gambit. The theoretically preferred line for Black is 1. e4 e5 2. f4 exf4 3. Nf3 d5! which immediately returns the pawn. On the other hand, in the main lines of the Benkö gambit, White holds a pawn advantage well into the late middlegame.
As for 2, I'm usually fine with having a material advantage, defending against an attack, simplifying and winning in the endgame. Other people like having the initiative and will usually try to return the gambited pawn in exchange for a (counter)attack.

7218: <p>Among chess players circulate the idea that any gambit should be accepted. It's an old and popular idea; if you don't want trouble, accept the gambit. Should this be consider a valid principle?</p>
 4362: <p>I think the way you put it this is pretty much just wrong.</p>

<p>There are a lot of pawn sacrifices in the opening that should not be accepted, something that is obscured by the fact that sacrifices that shouldn't be accepted are often not even called gambits (Though they still are gambits of course.)! The logic is along the lines "I play this move and now my opponent could win a pawn, but I know that he knows that that's no good, so I didn't actually sacrifice anything.". </p>

<p>Mostly sacrifices that are regularly accepted in tournament play are called gambits in the official nomenclature, but even among those, the best way to counter them is often to not take the pawn, or to return it as quickly as possible. </p>

<p>Certainly taking the pawn isn't usually the way to "avoid trouble".</p>

<p>The saying as I know it rather goes: "The best way to refute a gambit is to take the pawn." And I would interpret as meaning that if there is a refutation it is likely to be in the variations where you take the pawn. It does not mean whenever you take the pawn, there is going to be a refutation.</p>
 446: <p>I am not sure who may be these chessplayers who think gambits should be accepted. Certainly not the many (including most world top players) who do <strong>not</strong> reply with 2. ..., dc4 after 1. d4, d5 2. c4. </p>
 8160: <p>In addition to Glorfindel really good answer (+1) I would like to add that you can also use gambits to fill position with traps. The person who is not familiar with the gambit may get lost in the suddenly created 'minefield' position where a 'single step' from the right line of moves leads to a disaster. </p>

<p>It's also important to note that in many of the gambits you need to know how to decline it properly as well! 
Also there are some gambits that you SHOULD accept (to get a better position). For example Latvian, where after 1. e5 e5 2. Nf3 f5 the main line is 3. Ne5!? Even though you may know that it's the main line for white you really gotta be careful with your subsequent moves, because the position gets incredibly sharp, complicated. </p>
 9030: <p>Gambit's are sacrifices which are played hoping to get development advantage and/or initiative in opening.</p>

<p>So if you accept the gambit, and if the opponent can't consolidate development advantage and/or initiative, you will end up better. But if you decline, opponent will get advantage generally (This is where that principle comes from). Gambits are generally advantageous for sacrificer when they are declined.</p>

<p>However, some gambits really loses advantage when declined. For example:</p>

<pre><code>[FEN ""]
[Title "Smith-Morra Declined"]

1. e4 c5 2. d4 cxd4 3. c3 (3...dxc3 4.Nxc3 {White has development advantage, and is happy }) d3 4. Bxd3 { c3 is not available for White Knight, if
White plays c4, then whats that Bishop on d3 doing?}  ( 4. Qxd3 { White Bishop
is blocked and c3 is not available for White Knight.})  
</code></pre>

<p>Black simply expels White's fast development plan by declining the gambit. Now, White has opening problems to solve, not Black. </p>

<p>I play myself Smith-Morra with Whites, and hate it when declined. It's much more harder to play in declined variation.</p>

<p>So that principle is not valid. You should really think about the outcomes of accepting and declining before deciding.</p>
 7297: <p>This is really dependent on</p>

<ol>
<li>which gambit</li>
<li>the style of play you prefer.</li>
</ol>

<p>For 1, consider the King's Gambit. The <a href="https://chess.stackexchange.com/a/5882/7297">theoretically preferred line for Black</a> is 1. e4 e5 2. f4 exf4 3. Nf3 d5! which immediately returns the pawn. On the other hand, in the main lines of the Benkö gambit, White holds a pawn advantage well into the late middlegame.</p>

<p>As for 2, I'm usually fine with having a material advantage, defending against an attack, simplifying and winning in the endgame. Other people like having the initiative and will usually try to return the gambited pawn in exchange for a (counter)attack.</p>
