Board order in chess olympiads What's stopping teams in chess olympiads from mixing up their board order to gain an advantage? All I could find was the rules (http://www.fide.com/FIDE/handbook/chess_olympiad_regulations.pdf) that said that the board order couldn't be switched in between rounds. 

However, even without changing board order, being able to arrange the boards independently of playing strength can be used to gain an advantage. For example, suppose we had players A,B,C,D,D', where player A is stronger than player B, player B is stronger than player C, player C is stronger than player D, and player D is the same strength as player D'.

Instead of ordering the players by strength, we could put player D' at first board, and then place the remaining players by strength (so player A is second and so on). 

In each round, we only play four players. If we have the first board sit out, we could get the usual board order by playing strength. However, we could also have the fifth board sit out, in which case we have shifted our top three boards down by one, which could be useful against a stronger opponent (especially one that is top heavy). 



(Related question: Are the board positions of the 4 players of each country determined by Elo rating in chess olympiads?)
Well, in short, nothing. This (a tactical lineup) is actually quite common in team matches. There are basically two problems, the second of which is not a problem in the Olympiad because of the fixed board order.


Chess isn't an exact science; a weaker player can beat a stronger player (the odds that this happens are just lower). Given the ratings, you can calculate the expected score of a match where both teams are lined up in the regular way, and the expected score when one of the teams employs a tactical lineup. See below for some details.
If you do this too often, the opposing team can prepare and put their weakest player on board one (or even their second weakest player, putting their weakest player on board two, which results in them having a tactical lineup instead).


Here are some calculations based on the formula mentioned here for the expected score. As you see, the tactical lineup increases the expected score for the team by only 0.01 point.