Look out for who owns the building and who's giving the tour. Is it an owner operator? Live in? Big building? Operated by a management company? Basically you want to figure out how lecherous and shitty they're likely to be.

Also look at what if any utilities you're on the hook for and what appliances use what energy source and what they are. It's just always going to cost different amounts to heat your home with forced central air or cast iron radiators.