4 handed A7o bb defense

[Eihli]

unkown sb raises, i 3bet, he calls
flop Ks Qs 4d
I bet, he calls
turn 9s
I bet with no spade

my reasoning: any legit hand that he would raise with would have hit enough of that flop for him to play back at me so I think my turn bet will pick up the pot often enough to be +ev