Yes, there is the risk of e-transfer chargebacks. The thing that prevents Bisq users from doing that is probably the fact that Bisq is a reputation based system. Although you are anonymous on the system, you use the same nym all the time. You can see how many trades you've completed with the same trading partner and you can see how long (how many days) a trading partner's payment method had been "signed". To have a "signed" payment method, you need to used said payment method to buy bitcoin from a "signed" peer and wait 30 days after the trade is complete. As such, your reputation takes time to build up and it might matter if people want to do regular trades on the system; thus, disincentivizing rug-pulls. There are limits to not "signed" payment methods. See this page for details.

Comparatively, I find Robosats to be much more prone to fiat chargeback / rug-pulls, because you start with a new robot token each time and there is no indication of reputation. But I've only bought on both Bisq and Robosats, never tried selling; in other words, I had always been the guy sending fiat to other people and been the side able to pull off the rug-pull / able to initiate fiat chargebacks. As such, I cannot speak to how often fiat chargebacks happen; at least I've never done it.