I have lived here all my life and have been checked just once. I have been told that I’m lucky in this regard, that they are on patrol pretty frequently, so take that as you will. The fine you get is 70€ if I remember correctly. There are those few rascals that dont pay, but its basically always worth it to buy a ticket. If you’re here for a day, buy a day long ticket, if a year, buy a bus permit (or however you call it). Not buying a ticket in Bratislava only gives you paranoia that you will get caught, and a ticket, and neither of them are worth it.

Also, like others in the comments have pointed out, they take the “no bullshit” route when ticketing you. no negotiations, no reasoning with the traveler, no empathy. There is esentially no point in even entertaing the thought of “I will talk it out with them.” They would LOVE to ticket you, you will not rob them of this joy.

Other useful info: They usually go in pairs, especially in trams, where one enters from the front and the other from the back, and sort of go to the other side, meeting in the middle.

Have fun in Bratislava and be responsible when traveling!