Pocket pairs and AQ are good hands to flat preflop.
You can also 3b with them profitably sometimes too...
- Against BTN opens from villains who steal lots it can be more profitable to 3b small PP's than call to setmine - because their range contains weaker hands it will be harder to get paid if you hit s set.
- Against villains who call too many 3bets and play fit or fold on the flop you can 3bet AQ profitably.
Like you said, these are hands you should generally fold to a 4bet.