AJo BU/BB deep 5b pot

SB 3B is not small - 3x your raise.
BB'sc4B stat is irrelevant if sample size is small.
When BB 4b you should fold your hand right there.
POstflop you can bet smaller as pot is big enough.

Why do you play NL10 now?

You are right that the SB 3bet is small especially it is on NL10. I would suggest to everybody to make at least 8bb-s 3bet on the SB vs minraises on micro limit. But a lot of regs do this smaller 3bets, so if you don't have info about him, I wouldn't consider him to being weak. And after a cold4bet just fold. You haven't invested much money into the pot, so i would simply fold this hand right away. Postflop it is ok, but make a smaller cbet. You should do that in 4bet pots (1/2 cbets in 4bet pot IP are just too much)

easiest fold pre ever against the cold4b here. you're only reading what you want to read out of the situation, the facts are that bb's 4bet sizing is not small giving the other sizings and you don't have sample to make decent reads on anything other than his vpip/pfr, which are totally standard. deeper stacks make it so that you are in a terrible spot every time he doesn't fold and you can't really make assumptions regarding your fold equity.
as played, what gets there on the turn? 3 combos?

yes save yourself a lot of chips and just prefold here.. you will find better spots to get money from opponents.

Yup, this is fold pre. I think villains sizing doesn't matter so much, that cold 4bet is strong. AJo is not strong enough for us to start 5 betting.

5b bluff is too much and too expensive.

Thanks guys

In my opinion, you should have folded when the BB 4bet. AJ is an easily dominated hand in this situation and should fold.