What exactly determines how much the security deposit is?

In the past, I haven’t really cared about this, but now my only “live” wallet.dat has dangerously little BTC in it, so I’m starting to worry about almost not being able to make Bitcoin purchases in the future, since Bisq always requires some % as a security deposit.

But what exactly determines this amount? I thought it was fixed 30% for some reason, but it varies wildly between different trades.

Is it something that the Bitcoin seller sets? Is it determined based on the seller’s “history”/status? Or my own such? A combination of these?

Since SEPA bank transfers are the only method I can do, I’m very limited to basically just large bulk purchases each time.

You can set your deposit freely, down to minimum 0.001btc or 15% of trade amount, while the pre-set value is automatically calculated based on latest BTC volatility, to account for, and prevent, the risk of option buying from the offer taker, in a way that they would be unincentivized at canceling because the loss of the deposit would be above the loss of value of the trade.