I don't know what your standards are in terms of someone looking like "someone you'd want to marry" are, but if you think that the amount of depth most people want in a relationship with their partner is something that a non-trivial number of people could fake over a multiple year relationship, you're wildly off base. You're either grossly underestimating the degree of emotional connection that some people (including myself) would require for a long-term relationship or you're grossly overestimating the proportion of the dating pool who are highly skilled, manipulative sociopaths willing to spend years on con with a high risk of no payoff.