Yeah, but "suck" from our perspective and his perspective are two different things.
I can tell you whether a movie is going to suck (in my opinion) with a very high level of accuracy. I cannot tell you whether a movie is going to make money, because really shitty fucking movies make a whole ton of money on a regular basis, for reasons that escape me.
It will grant you that it is probably a lot easier to do if you have kids. Most movies I think that are really, really stupid and then I later find out someone went... I ask them why, and it's usually "Well, we didn't think it would be good but the kids seemed interested and it looked kid-safe and we all just really needed to get out of the house."