i've only said it when i meant it. totally depends on who's saying it... people define love in different ways, others may not have the same understanding of love that you might. but if someone says it to you, i think you should take it at face value.
unless they do something to make you think otherwise! feelings do change.
5 people have said they love me in my life, i believed them all... and to this day i have no reason to doubt that they did at the time.
hope that helps some.
