Generally, at 2nl, I find that most players won't adapt to your steals by light 3-betting. They'll just call, if they don't believe you. That holds for most players at the lowest levels. So, when I get 3-bet, I fold unless I believe I can get it in for value against a premium hand (AA or KK).
Now, if I had a few hundred or thousand hands on a person and I can see that they 3-bet from the blinds 9%+, that is a different story. Or if I have just been abusing a guy for an hour or so and suddenly he's 3-bet me from the blinds three times in a row, then I am going to suspect that this isn't always premium hands.
Still, A3o and KTs are easy folds. Well, I might 4-bet them because they have blockers but there's no real value in calling with them. I normally only 4-bet for value because very few players will fold once they have 3-bet. I have to know they're capable of folding their 3-bet to try a 4-bet bluff.
For hands where I have their range crushed but won't if I 4-bet, I call. This is hands like AQs, AK, JJ, KQs, and stuff like that. I will have position and a good hand. Be careful to not play these expecting to fold all the time if you don't hit. Calling a 3-bet then playing fit-or-fold is a good way to lose a lot of money.