It would help to know the motivation of the gambiteer. It never occurred to me to game the Swiss system, or that it was even gameable. Does the gambiteer want prize money? Rating points?
I've seen far too many Swiss systems at the class level where the winner had a perfect score. It's hard to believe that the goal is to win the tournament when the gambiteer voluntarily loses 1/2 point.
Let's start off by agreeing that surely, it is possible to get an easy 2nd and 3rd round if a player honestly loses or draws in the first round. The question becomes, can a cheater manipulate the system in a meaningful way.
So, let's assume for the SG (Swiss Gambit) to work:
1. it's a class-level tournament (my world.)
2. all players have the exact same rating.
3. the ratings are accurate.
I don't believe the SG would yield a positive result in this case; at best, the gambiteer would play people who might be off their games. However, it's much more likely he'd just be playing someone who lost. At the class level the games are almost always decisive.
Thus, I draw the conclusion that the SG only works dependably if there's a wide range of rated players. In large tournaments where players are grouped by class (D and under, C, B, A, Expert) I can't imagine a measurable result; the maximum difference between ratings is 200 points.
So, I posit:
1. it's a class-level tournament (my world.)
2. the brackets must include players of wildly different ratings
3. the ratings are accurate
4. the point of cheating is to get prize money
#1 implies draws are rare. This becomes important once the ratings are widely distributed. If the gambiteer secures the only draw, in round 1, he'll almost certainly end up playing in the "0-wins" bracket since the only other player with a draw would be his opponent and you can't be paired twice in a Swiss. And because of #2, the "0-wins" bracket will contain mostly lower rated players.
#2 implies a small tournament where there aren't enough players to fill out class-specific brackets.
#3 is a dicey assumption since I'd expect a cheater to sandbag his rating. I'd also expect a cheater to also play with a cheesy style designed to knock out less experienced players. For example I've seen players talk during play, make really fast moves in an attempt to psychologically rush the opponent, etc. This is probably not germane to the discussion, however.
#4 is my assumption of the motivation. This means the gambiteer wants to win the remainder of his games and be alone at the top. It doesn't do much good to get a cut of 3rd place with 5 other people. Because it's probably a small tournament (else #2 may not be true) the gambiteer needs very good score.
As I work through this, I begin to understand the SG. The SG exploits the Swiss method of
a. pairing people with the same scores
b. not allowing duplicate pairing, and
c. splitting the brackets in half by rating and pair the top of the top with the top of the bottom.
So the gambiteer scores a factional point in rd 1 in the hope he's always paired with someone in the group with the lesser score. So in round 2, he's paired with the "0/1" group. Further, he'll be paired with a player whose rating puts him in the middle of that group.
Consider the last round of a 5-round Swiss: The gambiteer, at 3.5 points, will be playing a middling 3.0 scorer. Compare this to the others at the top - two 4's battling it out. The Gambiteer is going to probably come out on top of one of them. The worst case scenario is that the 4's draw and all three of them share 1st, 2nd, and 3rd places.
Conclusion #1: I'm convinced it is easily possible to materially manipulate the 2nd round of tournaments that meet criteria #1 and #2.
Conclusion #2 - the SG is real in theory if dicey in practice. Draws, drop-outs, and the leeway allowed to the TDs can ruin the gambiteer's day.
Solution - group draws with the category above them, not below them. This will stop the SG in its tracks. That is, in rd 2, the gambiteer would be playing winners, not losers. Further, because of their scores, the gambiteer would be playing someone at the bottom of the top half of the group. Probably not the intent and certainly not a path to a prize-by-cheating. In fact the first-round draw works against him now as he always gets paired up. This may be too harsh. It could be in rds 2 and 4 the fractional scores would get paired up and in rd 3 they would get paired down.