When analyzing a prospective buy-and-hold, how do you account for super low rents?

[Kimberly T.]

Just curious what other investors do.  If you see a new rental come on the market for sale, and it has rents that are significantly below market (say, renting at 75% of market rate), how do you account for that when considering what kind of offer to make?

Assume, for sake of discussion, that the property is in average condition and could get market rent if a unit became vacant, and there is no rent control.