Lets say this hand comes up and it is the BB's first hand and he is an unknown.

I open in SB with AcKc and he calls.

4c3dQs...I bet, he raises and I call down what ends up being a 4c3dQs7s9h board....He shows 45.

Lets say two hours pass and we now have more info on this guy....He is super loose pre flop calling and cold calling a ton. He is not extremely agro pre but has raised a few times and showed down strong hands. I have seen him bet the river with extremely thin hands. I'm not sure if they were for value or as bluffs or perhaps that's just what he does. I've seen him 3 barrell a missed flush draw once. He doesn't seem overly bluffy. I have not seen him 3 bet pre flop.

Given this new info.....If we were to go back and play this hand again should we get away from our hand? If so when?

Assume hero is just a fantastic BVB player who is trying to get better.

I'd probably fold the turn. The only real draw got there.

I play it the same way as you did. Chill has a good point about the 56 getting there on the turn, but I think most of the time we have 6 clean outs and some nonzero % of the time we're actually ahead. If we think this guy likes to frequent Valuetown (a must see destination) I think we can fold the river.

Howd you get to show down the first, all the draws go there.

I'm not saying the straight is likely, but if he was semibluffing the flop, the most likely hand was 56. More likely that he has just a pair, but even with 6 clean outs you don't really have odds to call the turn.
Since he hasn't shown a tendency to bluff flop and turn but give up on the river, I don't see the point of calling turn to fold river.

I don't have a problem with seeing showdown as played with an unknown, but with the premise of what we know later I don't want to show down. If he can value bet bottom pair then he doesn't likely have a large bluffing range.

Good points, might be a spot for an exploitative turn fold. We are getting 5:1 on a turn call and if we do have 6 clean outs it's 6.7:1. We'd have to have a better hand ~ 5% of the time to make the call profitable (if my math is right), more so if some of our outs are dead of course. I agree, there aren't many semi-bluffs left, maybe something like A2 or A5, though our opponent could have some air balls. If he never has an air ball here, I agree, we can save some money and fold the turn.

The guy is unknown at the time, I beat all over card bluffs and airballs. This board isn't the worst board for him to attack. BVB situations bring out the bluff in people. People miss easy value bets all the time in my games on the river so I thought his range could be polarized.

I didn't feel great about the call down. I'd feel better if it was a super short game where we would get into this situation more often. Given that BVB situations are somewhat rare in my games maybe I should play in a more exploitative way.