If you're looking to make money in Old School RuneScape to buy the top items such as a Twisted Bow, staking is an option many people do for fun and money. Items like a Twisted Bow which some may consider essential for end-game PvM such as Raids 2 and Inferno, or whether you want to fund your PvP alts training and gear, nothing in the game comes at no cost. Realistically, if you want to buy a Twisted Bow, and make 4 million GP average at Vorkath - that's at least 300 (more like 350-400) hours of fighting the same boss just to get a Twisted Bow.
Staking is done by maxed melee accounts. Each stake must be within 10,000 coins to each other (and you can only use GP or Platinum Tokens), and in addition your winnings are taxed. From 0-10 million GP, you are taxed at 0.25%, 10-100 million 0.50% and 100 million upwards is taxed at 1.00%.
Because the accounts are all maxed melee and using the same weapon (abyssal) whip, your odds are set to be 50-50%, however you can still have the upper-hand by doing a few simple things.
One of the main things to do when you're looking to make money staking is to modify your attack style dependent on what stage you are currently at.
Lash: lash provides you with a +1 attack bonus, +1 strength and +1 defense. You will not see this in your stats screen as the attack styles do not display these bonuses visibly.
Flick: flick provides you a +3 attack bonus. This means you are far more accurate.
Deflect: when you deflect, as the name implies, you will get a +3 defensive bonus.
How can we use this to our advantage? The margins at most is between 1-2% however this 1-2% adds up in the long-run, and there's only two things you need to remember. When you're about to attack, swap to flick to get increased accuracy when hitting the opponent, even if you're both about to attack at the same time - flick has the best odds. When you've landed your attack and are about to be hit, swap to deflect to minimize any damage they may possibly land on you.
Many people choose to use staking/betting strategies. In real life at a casino, you have a maximum table limit and can not bet beyond that to prevent such strategies, however this is not the case in the duel arena. Unfortunately, taxation still exists and can make strategies less profitable.
Martingale is the most known strategy however it is only good if you have infinite money. Essentially, you keep on doubling anything you lose, and once you win you revert to your starting amount. This seems like a perfect strategy from a logical standpoint until you do the mathematics behind it and realize why people fail with it. The mathematical expectation from Martingale is 0 - you are free to run your own online tests (there are simulators that can do thousands of matches in seconds). Lucky Joe can easily win 10 times in a row and Unlucky Joe can easily lose 10 times in a row (this is bound to happen if you stake frequently). For context, 10 losses starting at 1 million GP adds up to a total loss of 1023 million GP, or 1 billion GP.
Martingale does work, but at the rate of 50-50 only. However with max losses in place in conjunction with Martingale, for example, 4 max losses and 4 rounds played, the probability of winning every round (until max losses) is 77%. The more max losses you can pocket the better, as long as you don't keep doubling down infinitely and restrict each round to a maximum number of losses. The limit on max losses is until the point taxation takes away from what you win in the end compared to what you've gambled in total.
The best advantage you have is with modifying your attack styles when staking and being cautious when staking your GP. If you want to make money staking, you realistically can not expect to win if you keep doubling down 10 times in a row, but what you can expect is an empty bank!
Best of luck with your staking at the Duel Arena!