How do you ensure success in a trade?

Sorry if it’s a dumb question, but I feel there’s no satisfactory answer. I’m a Bisq newbie.

So, let’s say that I want to trade $100 in cash, without intermediaries. I send money to my security deposit, the other person also sends money to their security deposit. Alright, so they say they’ll send me $100 once I send them the bitcoin. I do, and they send me a file with garbage.

How does the system gives a solution to such disputes?

this most definitely is not a bisq trade.

  • 100usd can be a very little amount considering miner fees
  • you don’t send btc to the buyer, you lock btc + deposit in escrow, when you confirm money received by buyer bisq will release btc
  • buyer will have to send the money first thing after they take the trade

So what happens if I receive actual cash, and decide to never send them the bitcoin? How can they prove they sent the money to have me punished?

Provability is key. You have (or can make it so you have) proof with practically every payment method, excluding F2F, where you don’t really need proof.

See the wiki for cash by mail trades. It recommends what buyers and sellers should do for proof about sending and receiving cash: Cash by mail - Bisq Wiki