How can you tell if a house is haunted?

Ok. Well my paraents are looking at a new houise to buy. It was built in 1930 something. Its on 2 1/2 acres. It also has three other horribly damaged houses on the property that are small and probably guest houses. Its been vacant for 2 or 3 years. If im not mistaken one person died in the house. I looked at the house today. It has no neighbors. Well it does but within 1/2 mile maybe. When we were in there it wasnt windy and doors would open by themselves. A window is broken/crashed. And my mom keeps teasing me this house it haunted. We discovered a secret pagway to the attic. When we tried to pull the ladder down it wouldnt budge. When we walked carefuly the floor felt really spongy and almost bouncy if you would say. I just wanna know if the house is haunted. Please give me some idead. Oh yea and if you want the adress is 20201 sw 280 st homestead, florida 33031