In your example, there's presumably a strong correlation between the users' (and their wealth) and their spending habits. That said, we probably could infer som

In your example, there's presumably a strong correlation between the users' (and their wealth) and their spending habits. That said, we probably could infer some things about the general population from that group. For one, they are part of the population. Two, there will be some similarities between their group and the complement of their group because humans have similar needs (e.g. groceries, gas, etc.). If you took this as your prior for the supergroup, then you would be more accurate than if you took a random number. There are no doubt differences between women on Okcupid and women in the general dating population. But in your example, we have a clear reason for believing that wealth is correlated with spending habits. If there is a reason why you believe Okcupid users should be as correlated with poor evaluation of the typical man, then it is at least not clear to me. Once again, using this data is likely far better than taking a random guess at how women in general evaluate the typical man.