Opinions concerning QT are one thing, but do remember some folks are lucky to have one/an/a single aquarium at all
If you decide to try a method without prophylactic medication like Paul B's method, do read as much about it as you can. It's not "do nothing and hope it turns out okay."
That may be true, but there are now options to buy quarantined fish. Sure they cost more, but do you want to do this cheap, or do this right? We’re dealing with living animals here, not nba cards.
I get this hobby isn’t cheap and people are doing it tough, but many of those same people that can’t afford/fit a QT tank/to QT go and buy a tank that is way too large for them to manage, and then start cutting costs and corners.
I’m not assuming that this is the case in this instance, but OP asked if you can manage the risks associated with not QTing a fish, and got an answer (which was no, which isn’t completely accurate either), but also was given the option of paying extra for qt’d fish.
we get upset at people who don’t look after their kids, dogs or cats properly so why shouldn’t this be any different?
For OP, any fish that isn’t QT’d is a gamble, QT helps stack the deck in your favour.
But if you’re willing to make the gamble (I wouldn’t), then sticking to healthy fish species with characteristics that reduce the risk of disease (large scales, thick slime coat) helps you feel more comfortable gambling. Notice I didn’t say reduce risks…
given the fish are 4 inches, I’m guessing they’re tangs, so none of what I mentioned before applies, good luck and hope it isn’t velvet if that’s the case!